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7 

ANCIENT 



AND 



MODERN ENGINEERING 



AND 



THE ISTHMIAN CANAL. 



WILLIAM H. BURR, C.E., 

Professor of Civil Engineering in Columbia University ; Member of the American Society of Civil Engineers 
and 0/ the Institution of Civil Engineers of Great Britain. 



FIRST EDITION. 
FIRST THOUSAND. 



NEW YORK : 

JOHN WILEY & SONS. 

London: CHAPMAN & HALL, Limited. 

1902. 



'Vfi^'LlBftARY-'oi* 



CONGRESS, 

Two Copits Rtoavec 

MOV. 29 fQ^9 
CnevuwHT entry 

CLASiS ^-'yXo Ho, 

U. L i> l-> 
corv B. 



Copyright, igoz, 

BY 

WILLIAM H. BURR. 



\ ■•' 



ROBERT DRUMMOND, PRINTER, NEW YORK, 



INTRODUCTION. 



This book is the outcome of a course of six lectures delivered 
at the Cooper Union in the city of New York in February and 
March, 1902, under the auspices of Columbia University. It- 
seemed desirable by the President of the University that the 
subject-matter of the lectures should be prepared for ultimate 
publication. The six Parts of the book, therefore, comprise the 
substance of the six lectures, suitably expanded for the purposes 
of publication. 

It may be interesting to state that the half-tone illustrations 
have, with scarcely-an exception, been prepared from photo- 
graphs of the actual subjects illustrated. All such illustrations 
in Parts V and VI devoted to the Nicaragua and Panama Canal 
routes are made from photographs at the various locations by 
members of the force of the Isthmian Canal Commission; they 
are, therefore, absolutely true representations of the actual local- 
ities to which they apply. 

For other illustrations the author wishes to express his in- 
debtedness to Messrs. G. P. Putnam's Sons, Messrs. Turneaure 
and Russell, John Wiley & Sons, The Morrison -Jewell Filtration 
Company, Mr. H. M. Sperry, Signal Engineer, The Engineering 
News, The Railroad Gazette, The American Society of Civil 
Engineers, The Standard Switch and Signal Company, The 



iv INTRODUCTION, 

Baldwin Locomotive Works, The American Locomotive Works, 
and the International Pump Company, and to others from 
whom the author has received courtesies which he deeply 
appreciates. 

The classification or division of the matter of the text, and 
the table of contents, have been made so complete, with a view 
to convenience even of the desultory reader in seeking any par- 
ticular subject or paragraph, that no index has been prepared, 
as it is believed that the table of contents, as arranged, practi- 
'cally supplies the information ordinarily given by a comprehen- 
;sive index. 

Complete and detailed treatments of the purely technical 

miatters covered by Part II will be found in the author's 

"Elasticity and Resistance of Materials" and in his "Stresses 

in Bridge and Roof Trusses, Arched Ribs and Suspension 

Bridges." 

W. H. B. 

Columbia University, 
October 24, 1902. 



CONTENTS. 



PART I. 

ANCIENT CIVIL-ENGINEERING WORKS. 
CHAPTER I. 

ART. PAGE 

1. Introductory , i 

2. Hydraulic Works of Chaldea and Egj'pt 2 

3. Structural Works in Chaldea and Egypt a 

■ 4. Ancient Maritime Commerce y 

5. The Change of the Nile Channel at Memphis g 

6. The Pyramids g 

7. Obelisks, Labyrinths, and Temples 12 

8. Nile Irrigation i -^ 

9. Prehistoric Bridge-building i^ 

10. Ancient Brick-making jc 

1 1. Ancient Arches 16 

CHAPTER II. 

12. The Beginnings of Engineering Works of Record ig 

13. The Appian Way and other Roman Roads 20 

14. Natural Advantages of Rome in Structural Stones 22 

15. Pozzuolana Hydraulic Cement 24 

16. Roman Bricks and Masonry 25 

1 7. Roman Building Laws 27 

18. Old Roman Walls 27 

19. The Servian Wall 28 

20. Old Roman Sewers 29 

21. Early Roman Bridges 31 

22. Bridge of Alcantara 3 c 

23. Military Bridges of the Romans 3^ 

24. The Roman Arch 36 

V 



Tl CONTENTS. 



CHAPTER III. 

ART. PAGE 

25. The Roman Water-supply 37 

26. The Roman Aqueducts 38 

27. Anio Vetus 39 

28. Tepula 40 

29. Virgo 40 

30. Alsietina 40 

31. Claudia ^ 41 

32. Anio Novus 42 

33. Lengths and Dates of Aqueducts ... , . 42 

34. Intakes and Settling-basins 43 

35. Delivery -tanks 44 

36. Leakage and Lining of Aqueducts 44 

37. Grade of Aqueduct Channels 45 

38. Qualities of Roman Waters 46 

39. Combined Aqueducts 46 

40. Property Rights in Roman Waters 46 

.41. Adjutages and Unit of Measurement . 47 

42. The Stealing of Water 49 

43. Aqueduct Alignment and Design of Siphons 49 



CHAPTER IV. 

44. Antiquity of Masonry Aqueducts 52 

45. Pont du Gard 52 

46. Aqueducts at Segovia, Metz, and other Places 53 

47. Tunnels 54 

48. Ostia, the Harbor of Rome 56 

49. Harbors of Claudius and Trajan 58 

CHAPTER V. 

50. Ancient Engineering Science 60 

51. Ancient Views of the Physical Properties of Materials 61 

52. Roman Civil Engineers Searching for Water 62 

53. Locating and Designing Conduits 63 

54. Siphons 64 

55. Healthful Sites for Cities 65 

56. Foundations of Structures 65 

5 7. Pozzuolana and Sand 66 

58. Lime Mortar 66 

59. Roman Bricks according to Vitruvius 66 

60. Roman Timber 67 

61. The Rules of Vitruvius for Harbors 67 

62. The Thrusts of Arches and Earth ; Retaining-walls and Pavements 68 

63. The Professional Spirit of Vitruvius 68 

64. Mechanical Appliances of the Ancients 69 

65. Unlimited Forces and Time 69 



CONTENTS. VI 1 

PART II. 

BRIDGES. 
CHAPTER VI. 

ART. PAGE 

66. Introductory „ 70 

67. First Cast-iron Arch 70 

68. Early Timber Bridges in America 71 

69. Town Lattice Bridge 72 

70. Howe Truss 74 

71. Pratt Truss 76 

72. Squire Whipple's Work 77 

73. Character of Work of Early Builders 77 

CHAPTER VII. 

74. Modern Bridge Theory 78 

75. The Stresses in Beams 7^ 

76. Vertical and Horizontal Shearing Stresses 80 

77. Law of Variation of Stresses of Tension and Compression 82 

78. Fundamental Formulae of Theory of Beams 83 

79. Practical Applications 85 

80. Deflection 86 

81. Bending Moments and Shears with Single Load 87 

82. Bending Moments and Shears with any System of Loads 89 

83. Bending Moments and Shears with Uniform Loads 92 

84. Greatest Shear for Uniform Moving Load 94 

85. Bending Moments and Shears for Cantilever Beams 96 

86. Greatest Bending Moment with any System of Loading 97 

87. Applications to Rolled Beams. gg 

CHAPTER VIIL 

88. The Truss Element or Triangle of Bracing 100 

89. Simple Trusses 101 

90. The Pratt Truss Type 102 

91. The Howe Truss Type 105 

92. The Simple Triangular Truss 106 

93. Through- and Deck- Bridges. 108 

94. Multiple Systems of Triangulation 108 

95. Influence of Mill and Shop Capacity on Length of Span 109 

96. Trusses with Broken or Inclined Chords 109 

97. Position of any Moving Load for Greatest Webb Stress no 

98. Application of Criterions for both Chord and Web Stresses m 

99. Influence Lines 112 

100. Influence Lines for Moments both for Beams and Trusses 113 

loi. Influence Lines for Shears both for Beams and Trusses 1 15 

102. Application of Influence-line Method to Trusses ■_. 118 



vui CONTENTS. 

CHAPTER IX. 

ART. PAGE 

103. Lateral Wind Pressure on Trusses 122 

104. Upper and Lower Lateral Bracing 124 

105. Bridge Plans and Shopwork. 125 

106. Erection of Bridges 126 

107. Statically Determinate Trusses 126 

108. Continuous Beams and Trusses — Theorem of Three Moments 128 

109. Application to Draw- or Swing-bridges 130 

1 10. Special Method for Deflection of Trusses 130 

111. Application of Method for Deflection of Triangular Frame 133 

112. Application of Method for Deflection to Truss 134 

113. Method of Least Work 137 

1 14. Application of Method of Least Work to General Problem 138 

115. Application of Method of Least Work to Trussed Beam 139 

116. Removal of Indetermination by Methods of Least Work and Deflection 141 

CHAPTER X. 

117. The Arched Rib, of both Steel and Masonry 142 

118. Arched Rib with Ends Fixed 144 

1 19. Arched Rib with Ends Jointed 144 

120. Arched Rib v/ith Crown and Ends Jointed 145 

121. Relative Stiffness of Arched Ribs 145 

122. General Conditions of Analysis of Arched Ribs 146 

CHAPTER XL 

123. Beams of Combined Steel and Concrete 149 

CHAPTER Xn. 

1 24. The Masonry Arch 154 

125. Old and New Theories of the Arch 155 

126. Stress Conditions in the Arch-ring 1^8 

127. Applications to an Actual Arch ic8 

128. Intensities of Pressure in the Arch-ring 162 

129. Permissible Working Pressures 163 

130. Largest Arch Spans i6j 

CHAPTER XIII. 

131. Cantilever and Stiffened Suspension Bridges , , , 166 

132. Cantilever Bridges 166 

133. Stiffened Suspension Bridges 168 

134. The Stiffening Truss , 170 

135. Location and Arrangement of Stiffening Trusses 171 

136. Division of Load between Cables and Stiffening Truss 173 

137. Stresses in Cables and Moments and Shears in Trusses 174 

138. Thermal Stresses and Moments in Stiffened Suspension Bridges I7e 

139. Formation of the Cables iy5 

140. Economical Limits of Spans 177 



CONTENTS. IX 

PART III. 

WATER-WORKS FOR CITIES AND TOV/NS. 

CHAPTER XIV. 

ART. PACK 

141. Introductory 179 

142. First Steam-pumps 180 

143. Water-supply of Paris and London 181 

144. Early Water-pipes. 181 

145. Earliest Water-supplies in the United States 182 

146. Quality and Uses of Public Water-supply 182 

147. Amount of Public Water-supply 183 

148. Increase of Daily Consumption and the Division of that Consumption 183 

149. Waste of Public Water 186 

150. Analysis of Reasonable Daily Supply per Head of Population 188 

151. Actual Daily Consumption in Cities of the United States 189 

152. Actual Daily Consumption in Foreign Cities 191 

X53. Variations in Rate of Daily Consumption 192 

154. Supply of Fire-streams . ; 193 

CHAPTER XV. 

155. Waste of Water, Particularly in the City of New York 196 

156. Division of Daily Consumption in the City of New York 197 

157. Daily Domestic Consumption 198 

158. Incurable and Curable Wastes 199 

159. Needless and Incurable Waste in City of New York 200 

160. Increase in Population 200 

161. Sources of Public Water-supplies 202 

162. Rain-gauges and their Records 204 

163. Elements of Annual and Monthly Rainfall , 204 

164. Hourly or Less Rates of Rainfall 207 

165 . Extent of Heavy Rain-storms 207 

166. Provision for Low Rainfall Years 208 

167. Available Portion of Rainfall or Run-off of Watersheds 209 

168. Run-off of Sudbury Watershed 211 

169. Run-off of Croton Watershed 211 

170. Evaporation from Reservoirs 213 

J.71. Evaporation from the Earth's Surface 215 

CHAPTER XVI. 

172. Application of Fitzgerald's Results to the Croton Watershed 216 

173. The Capacity of the Croton Watershed 217 

/74. Necessary Storage for New York Supply to Compensate for Deficiency 218 

175. No Exact Rule for Storage Capacity 220 

176. The Color of Water 221 

177. Stripping Reservoir Sites 222 



X CONTENTS. 

ART. PAGE 

178. Average Depth of Reservoirs should be as Great as Practicable 224 

179. Overturn of Contents of Reservoirs Due to Seasonal Changes of Temperature. . 224 

180. The Construction of Reservoirs . 225 

181. Gate-houses, and Pipe-lines in Embankments 229 

182. High Masonry Dams 230 

CHAPTER XVII. 

183. Gravity Supplies 234 

184. Masonry Conduits 234 

185. Metal Conduits - . . 236 

186. General Formula for Discharge of Conduits— Chezy's Formula 237 

187. Kutter's Formula 239 

188. Hydraulic Gradient 241 

189. Flow of Water in Large Masonry Conduits 244 

190. Flow of Water through Large Closed Pipes 245 

191. Change of Hydraulic Gradient by Changing Diameter of Pipe 250 

192. Control of Flow by Gates at Upper End of Pipe-line 25 1 

193. Flow in Old and New Cast-iron Pipes — Tubercles 25 1 

194. Timber-stave Pipes , 253 

CHAPTER XVIII. 

195. Pumping and Pumps 254 

196. Resistances of Pumps and Main — Dynamic Head 258 

197. Duty of Pumping-engines 260 

198.. Data to be Observed in Pumping-engine Tests 261 

199. Basis of Computations for Duty 262 

200. Heat-units and Ash in 100 Pounds of Coal, and Amount of Work Equivalent to 

a Heat-unit 262 

201. Three Methods of Estimating Duty 265 

202. Trial Test and Duty of Allis Pumping-engine 265 

203. Conditions Affecting Duty of Pumping-engines 266 

204. Speeds and Duties of Modern Pumping-engines 266 

CHAPTER XIX. 

205. Distributing-reservoirs and their Capacities 267 

206. System of Distributing Mains and Pipes 268 

207. Diameters of and Velocities in Distributing Mains and Pipes 269 

208. Required Pressures in Mains and Pipes 270 

209. Fire-hydrants 270 

2 10. Elements of Distributing Systems 270 

CHAPTER XX. 

211. Sanitary Improvement of Public Water-supplies 276 

212. Improvement by Sedimentation 277 

213. Sedimentation Aided by Chemicals 279 

214. Amount of Sulid Matter Removed by Sedimentation 279 

215. Two Methods of Operating Sedimentation-basins 279 



CONTENTS. xi 

ART. PAGE 

2i6. Sizes and Construction of Settling-basins 280 

217. Two Methods of Filtration 281 

218. Conditions Necessary for Reduction of Organic Matter 282 

219. Slow Filtration through Sand — Intermittent Filtration 283 

220. Removal of Bacteria in the Filter 286 

221. Preliminary Treatment — Sizes of Sand Grains 286 

222. Most Effective Sizes of Sand Grains 288 

223. Air and Water Capacities 288 

224. Bacterial Efficiency and Purification — Hygienic Efficiency 290 

225. Bacterial Activity near Top of Filter 290 

226. Rate of Filtration 291 

227. Effective Head on Filter 291 

228. Constant Rate of Filtration Necessary 292 

229. .Scraping of Filters 293 

230. Introduction of Water to Intermittent Filters 294 

231. Effect of Low Temperature 294 

232. Choice of Intermittent or Continuous Filtration 294 

233. Size and Arrangement of Slow Sand Filters 295 

234. Design of Filter-beds 296 

235. Covered Filters 299 

236. Clear-water Drain-pipes of Filters 299 

237. Arrangement of the Sand at Lawrence and Albany 300 

238. Velocity of Flow through Sand 302 

239. Frequency of Scraping and Amount Filtered between Scrapings 303 

240. Cleaning the Clogged Sand 303 

241. Controlling or Regulating Apparatus 305 

242. Cost of Slow Sand Filters 307 

243. Cost of Operation of Albany Filter 308 

244. Operation "and Cost of Operation of Lawrence Filter 309 

245. Sanitary Results of Operation of Lawrence and Albany Filters 310 

246. Rapid Filtration with Coagulants 311 

247. Operation of Coagulants 312 

248. Principal Parts of Mechanical Filter-plant — Coagulation and Subsidence 313 

249. Amount of Coagulant — Advantageous Eifect of Alum on Organic Matter 314 

250. High Heads and Rates for Rapid Filtration 315 

25 1. Types and General Arrangement of Mechanical Filters 316 

252. Cost of Mechanical Filters 318 

253. Relative Features of Slow and Rapid Filtration 318 



PART IV. 

SOAfE FEATURES OF RAILROAD ENGINEERING. 

CHAPTER XXI. 

254. Introductory 320 

255. Train Resistances 322 

256. Grades 322 



xii CONTENTS. 

ART. PAGE 

257. Curves 324 

258. Resistance of Curves and Compensation in Grades 324 

259. Transition Curves 325 

260. Road-bed, including Ties 327 

261. Mountain Locations of Railroad Lines , 328 

262. The Georgetown Loop 331 

263. Tunnel-loop Location, Rhaetian Railways, Switzerland 331 

CHAPTER XXIL 

264. Railroad Signalling 335 

265. The Pilot Guard 335 

266. The Train Staff. 335 

267. First Basis of Railroad Signalling , 336 

268. Code of American Railway Association 337 

268«. The Block 338 

269. Three Classes of Railroad Signals 338 

270. The Banner Signal 338 

271. The Semaphore .... 340 

272. Colors for Signalling 340 

273. Indications of the Semaphore 341 

274. General Character of Block System 342 

275. Block Systems in Use 343 

276. Locations of Signals 344 

277. Home, Distant, and Advance Signals , 344 

278. Typical Working of Auto-controlled Manual Systeim 345 

279. General Results 348 

280. Distant Signals 349 

281. Function of Advance Signals 349 

282. Signalling at a Single-track Crossing 350 

283. Signalling at a Double-track Crossing 352 

284. Signalling for Double-track Junction and Cross-over 352 

285. General Observations 353 

286. Interlocking-machines 354 

287. Methods of Applying Power in Systems of Signalling 357 

288. Train-staff Signalling 358 

CHAPTER XXni. 

289. Evolution of the Locomotive 363 

290. Increase of Locomotive Weight and Rate of Combustion of Fuel 365 

291. Principal Parts of a Modern Locomotive 366 

292. The Wootten Fire-box and Boiler , 367 

293. Locomotives with Wootten Boilers 370 

294. Recent Improvements in Locomotive Design 372 

295. Compound Locomotives with Tandem Cylinders 373 

296. Evaporative Efficiency of Different Rates of Combustion 375 

296a. Tractive Force of a Locomotive 376 

297. Central Atlantic Type of Locomotive 378 

298. Consolidation Engine, N. Y. C. & H. R. R. R 379 



CONTENTS. Xlll 

ART, PAGE 

299. P. , B. & L. E. Consolidation Engine 380 

300. L. S. & M. S, Fast Passenger Engine 381 

301. Northern Pacific Tandem Compound Locomotive 382 

302. Union Pacific Vauclain Compound Locomotive 384 

303. Southern Pacific Mogul with Vanderbilt Boiler 384 

304. The ' ' Soo " Decapod Locomotive 385 

305. The A., T. & S. F. Decapod, the Heaviest Locomotive yet Built 386 

306. Comparison of Some of the Heaviest Locomotives in Use 389 



PART V. 

THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

Feasibility of Nicaragua Route 390 

Discovery of Lake Nicaragua 350 

Early Maritime Commerce, with Lake Nicaragua. 391 

Early Examination of Nicaragua Route 392 

English Invasion of Nicaragua 392 

Atlantic and Pacific Ship-canal Company 392 

Survey and Project of Col. O. W. Childs 393 

The Project of the Maritime Canal Company , 353 

The Work of the Ludlow and Nicaragua Canal Commissions 394 

The Route of the Isthmian Canal Commission 395 

Standard Dimensions of Canal Prism 39$ 

The San Juan Delta 397 

The San Carlos and Serapiqui Rivers 398 

The Rapids and Castillo Viejo 399 

The Upper San Juan 399 

The Rainfall from Greytown to the Lake 399 

Lake-surface Elevation and Slope of the River 400 

Discharges of the San Juan, San Carlos, Serapiqui 401 

Navigation on the San Juan 401 

The Canal Line through the Lake and Across the West Side 402 

Character of the Country West of the Lake 403 

Granada to Managua, thence to Corinto 404 

General Features of the Route 404 

Artificial Harbor at Greytown 405 

Artificial Harbor at Brito 407 

From Greytown Harbor to Lock No. 2 408 

From Lock No. 2 to the Lake 409 

Fort San Carlos to Brito 410 

Examinations by Borings 411 

Classification and Estimate of Quantities 412 

Classification and Unit Prices 413 

Curvature of the Route 413 



XIV CONTENTS. 

ART. PAGE 

339. The Conchuda Dam and Wasteway 414 

340. Regulation of the Lake Level 417 

341. Evaporation and Lockage 418 

342. The Required Slope of the Canalized River Surface 419 

343. All Surplus Water to be Discharged over the Conchuda Dam 419 

344. Control of the Surface Elevation of the Lake 420 

345. Greatest Velocities in Canalized River 425 

346. Wasteways or Overflows 427 

347. Temporary Harbors and Service Railroad 427 

348. Itemized Statement of Length and Cost 427 



PART VI. 

THE PANAMA ROUTE FOR A SHIP CANAL. 

349. The First Panama Transit Line , 429 

350. Harbor of Porto Bello Established in 1597 429 

351. First Traffic along the Chagres River, and the Importance of the Isthmian 

Commerce 431 

352. First Survey for Isthmian Canal Ordered in 1520 431 

353. Old Panama Sacked by Morgan and the Present City Founded 431 

354. The Beginnings of the French Enterprise 432 

355. The Wyse Concession and the International Congress of 1870 432 

356. The Plan without Locks of the Old Panama Canal Company 433 

357. The Control of the Floods in the Chagres 434 

358. Estimate of Time and Cost — Appointment of Liquidators 435 

359. The "Commission d'Etude" , 43c 

360. Extensions of Time for Completion 436 

361. Organization of the New Panama Canal Company, 1894 437 

362. Priority of the Panama Railroad Concession 437 

363. Resumption of Work by the New Company — The Engineering Commission and 

the Comite Technique 438 

364. Plan of the New Company 439 

365. Alternative Plan of the New Panama Canal Company 440 

366. The Isthmian Canal Commission and its Work 441 

367. The Route of the Isthmian Canal Commission that of the New Panama Canal 

Company 441 

368. Plan for a Sea-level Canal 443 

369. Colon Harbor and Canal Entrance 443 

370. Panama Harbor and Entrance to Canal 444 

371. The Route from Colon to Bohio 44c 

372. The Bohio Dam 446 

373. Variation in Surface Elevation of Lake 448 

374. The Extent of Lake Bohio and the Canal Line in It , 448 

375. The Floods of the Chagres , 44Q 



CONTENTS. XV 

A'<T. PAGE 

376. The Gigante Spillway or Waste-weir 450 

377. Storage in Lake Bohio for Driest Dry Season 45 1 

378. Lake Bohio as a Flood Controller 452 

379. Effect of Highest Floods on Current in Channel in Lake Bohio 453 

380. Alhajuela Reservoir not Needed at Opening of Canal 453 

381. Locks on Panama Route 454 

382. The Bohio Locks 4C4 

383. The Pedro Miguel and Miraflores Locks 454 

384. Guard-gates near Obispo 4^5 

385. Character and Stability of the Culebra Cut 455 

386. Length and Curvature 456 

387. Small Diversion-channels 457 

388. Principal Items of Work to be Performed 457 

389. Lengths of Sections and Elements of Total Cost. 458 

390. The Twenty Per Cent Allowances for Exigencies 459 

391. Value of Plant, Property, and Rights on the Isthmus 460 

392. Offer of New Panama Coal Company to Sell for $40,000,000 461 

393. Annual Costs of Operation and Maintenance 462 

394. Volcanoes and Earthquakes 4^3 

395. Hygienic Conditions on the Two Routes. 464 

396. Time of Passage Through the Canal. , 465 

397. Time for Completion on the Two Routes 466 

398. Industrial and Commercial Value of the Canal 469 

399. Comparison of Routes o 471 



PART I. 

ANCIENT CiyiL-ENGINEERING WORKS. 



CHAPTER I. 

I. Introductory. — It' is a common impression even among 
civil engineers that their profession is of modern origin, and it is 
frequently called the youngest of the professions. That impres- 
sion is erroneous fromi every point of view. Many engineering 
works of magnitude and of great importance to the people whom 
they served were executed in the very dawn of history, and they 
have been followed by many other works of at least equal mag- 
nitude and under circumstances scarcely less noteworthy, of 
which we have either remains or records. During the lapse 
of the arts and of almost every process of civilization throughout 
the darkness of the Middle Ages there was little if any progress 
made in the art of the engineer, and what little was done was 
executed almost entirely under the name of architecture. With 
the revival of intellectual activity and with the development 
of science the value of its practical application to the growing 
nations of the civilized world caused the modem profession of 
civil engineering to take definite shape and to be known by the 
name which it now carries, but which was not known to ancient 
peoples. Unfortunately the beginnings of engineering cannot 
be traced ; there is no historical record running back far enough 
to render account of the earhest engineering works whose ruins 
remain as enduring evidence of what was then accomplished. 



"2 ANCIENT CIVIL-ENGINEERING WORKS. 

It is probably correct to state that the material progress of 
any people has always been concurrent with the development 
of the art of civil engineering, and, hence, that the practice of 
civil engineering began among the people who made the earliest 
progress in civilization, to whom ' ' the art of directing the Great 
Sources of Power in Nature for the iise and convenience of mian" 
became an early and imperative necessity. Indeed that con- 
•clusion is confirmed by the most ancient ruins of what may be 
termed public works that archaeological investigations have 
revealed to us, among which are those to be found in the Chal- 
dean region, in India, and in Egypt. Obviously, anything like a 
detailed account of the structural and other works of such ancient 
character must be lacking, as some of them were built before even 
the beginnings of history. Our only data, therefore, are the 
remains of such works, and unfortunately they have too fre- 
quently been subject to the destructive operations of both man 
and nature. 

2. Hydraulic Works of Chaldea and Egypt. — It is absolutely 
certain that the populous centres of prehistoric times could not 
have existed nor have been served with those means of com- 
munication imperatively necessary to their welfare without the 
practice of the art of engineering, under whatever name they 
may have applied to it. It is known beyond any doubt that 
the anciently populous and prosperous country at the head of 
the Persian Gulf and watered by the Euphrates and the Tigris 
was irrigated and served by a most complete system of canals, 
and the same observation can be made in reference to the valley 
of the Nile. It is not possible at this period of that country's 
history to determine to what extent irrigation was practised or 
how extensively the former country was served by water trans- 
portation conducted along artificial channels; but hydraulic 
works, including dams and sluices with other regulating appliances 
designed to bring waters from the rivers on to the land, were 
certainly among the earliest executed for the benefit of the com- 
miunities inhabiting those regions. The remains of those works, 
spread over a large territory in the vicinity of ancient Babylon, 
Nippur, and other centres of population, show beyond the slight- 
est doubt that there existed a network of water communication 



HYDRAULIC WORKS OF CHALDEA AND EGYPT. 



throughout what was in those days a country rich in agricultural 
products and which supported the operations of a most pros- 



V^, 



CHALDEA 

AND NEIGHBORING COUNTRIES 




perous commerce. These canals were of ample dimensions to 
float boats of no mean size, although much smaller than those 
occupied in our larger systems of canal transportation. They 



4. ANCIENT CIVIL-ENGINEERING WORKS. 

were many miles in length, frequently interlacing among them- 
selves and intersecting both the Tigris and the Euphrates. 
The remains of these canals, some of them still containing water, 
show that they must originally have been filled to depths vary- 
ing from five or six to fifteen or twenty feet, and that their widths 
may have been twenty-five or thirty feet or more. Another 
curious feature is their occasional arrangement in twos and threes 
alongside of each other with embankments only between. The 
entire Euphrates-Tigris valley from the head of the Persian Gulf 
at least to modern Baghdad (i.e.. Babylonia) and possibly to 
ancient Nineveh was served by these artificial waterways. Later, 
when Alexander the Great made one of his victorious expeditions 
through the Assyrian country, he found in the Tigris obstructions 
to the passage of his ships down-stream in the shape of masonry 
dams. This was between 356 and 322 B.C. These substantial 
dams Ysfere built across the river for the purpose of intakes to 
irrigating-canals for the benefit of the adjacent country. These 
canals, like those of Egypt, were fitted with all the necessary 
regulating-devices of sluices or gates, both of a crude character, 
but evidently sufficiently effective for their purpose. 

It is known that there were in those early days interchanges 
of large amounts and varieties of commodities, and it is almost 
if not quite certain that the countries tributary to the Persian 
Gulf not only produced sufficient grain for their own needs, but 
also carried on considerable commerce with the Asiatic coast. 
We have no means of ascertaining either the volume or the pre- 
cise character of the traffic, but there is little or no doubt of its 
existence. It is established also that the waters of the Red Sea i 
and the Nile were connected by a canal about 1450 e.g. Recent ' 
investigations about Nippur and other sites of ancient cities in 
that region confirm other indications that the practice of some 
branches of hydraulic engineering had received material develop- 
ment from possibly two to four thousand years before the Chris- 
tian era. 

3. Structural Works in Chaldea and Egypt. — The ruins of 
ancient buildings which have been unearthed by excavations in 
the same vicinity show with the same degree of certainty that 
the art of constructing buildings of considerable dimensions had 



STRUCTURAL WORKS IN CHALDEA AND EGYPT. 5 

also made material progress at the same time, and in many cases 
must have involved engineering considerations of a decided 
character both as to structural materials and to foundations. 
Bricks were manufactured and used. Stones were quarried 
and dressed for building purposes and applied so as to produce 
structural results of considerable excellence. Even the arch 
was probably used to some extent in that locality in those early 
days, but stone and timber beams were constantly employed. 
In the prehistoric masonry constructions of both the Egyptians 
and Chaldeans and probably other prehistoric peoples, lime 
or cement mortar was not employed, but came into use at a sub- 
sequent period when the properties of lime and cement as cement- 
ing materials began to be recognized. The first cementing 
material probably used in Egypt was a sticky clay, or possibly a 
calcareous clay or earth. The same material was also used in 
the valley of the Euphrates, but in the latter country there are 
springs of bitumen, where that material exudes from the earth 
in large quantities. The use of this asphaltic cement at times 
possibly involved that of sand or gravel in some of the early 
constructions. Later, lime mortar and possibly a weak hydraulic 
cement came to be employed, although there is little if any evi- 
dence of the latter material. 

Iron was manufactured and used at least in small quantities, 
and for some structural purposes, even though in a crude manner. 
Bituminous or other asphaltic material was found as a natural 
product at various points, and its value for certain structural 
purposes was well known; it was used both for waterproofing 
and for cement. It is practically certain that the construction 
of engineering works whose interesting ruins still remain involved 
a considerable number of affiliated engineering operations of 
which no evidence has yet been found, and of the employment 
of tools and appliances of which we have no record. So far as 
these works were of a public character they were constructed 
by the aid of a very different labor system from that now existing. 
The kings or ruling potentates of those early times were clothed 
with the most arbitrary authority, sometimes exercised wisely 
in the best interests of their people, but at other times the ruling 
motive was selfishness actuated by the most intense egotism 



6 



ANCIENT CIVIL-ENGINEERING WORKS. 



and brutal tyranny. Hence all public works were executed 
practically as royal enterprises and chiefly by forced labor, per- 
haps generally without compensation except mere sustenance. 
Under such conditions it was possible to construct works on a 
scale out of all proportion to national usefulness and without 
structural economy. When it is remembered that these con- 
ditions existed without even the shadow of engineering science, 
it is obvious that structural economy or the adaptation of well- 
considered means to an end will not be found to characterize 
engineering operations of prehistoric times. Nevertheless there 
are evidences of good judgment and reasonable engineering 
design found in connection with some of these works, particularly 
with those of an hydraulic character. Water was lifted or 
pumped by spiral or screw machines and by water-wheels, and 
it is not improbable that other appliances of power served the 
purposes of many industrial and crude manufacturing opera- 
tions which it is now impossible for us to determine. 




Fig. I. — Home Built on Piles in the Land of Punt. 

It is an interesting fact that while many ancient works were 
exceedingly massive, like the pyramids, the largest of those of 
which the ruins have been preserved seldom seem to show little 
or any evidence of serious settlement. Whether the ancients 
had unusually sound ideas as to the design of foundation works, 
or whether those only have come down to us that were founded 
directly upon rock, we have scarcely any means of deciding. 
Nor can we determine at this time what special recourses were 
available for foundation work on soft ground. Probably one 



ANCIENT MARITIME COMMERCE. 7 

of the earliest recognized instances, if not the earhest, of the 
building of structures on piles is that given by Sir George Raw- 
linson, when he states that a fleet of merchant vessels sent down 
the northeast African coast by the Egyptian queen Hatasu, 
probably 1700 b.c. or 1600 b.c, found a people whose huts were 
supported on piles in order to raise them above the marshy ground 
and possibly for additional safety. A representation (Fig. i) of 
one of these native homes on piles is found among Egyptian 
hieroglyphics of the period of Queen Hatasu. 

4. Ancient Maritime Commerce. — It is well known that both 
the Chaldean region and the Nile valley and delta, at least from 
Ethiopia to the Mediterranean Sea, were densely populated dur- 
ing the period of two to four or five thousand years before the 
Christian era. By means of the irrigation works to which refer- 
ence has already been made both lands became highly productive, 
and it is also well known that those peoples carried on a consider- 
able commerce with other countries, as did the Phoenicians also, 
at least between the innumerable wars which seemed to be 
the main business of states in those days. These commercial 
operations required not only the construction of fleets of what 
seem to us small vessels for such purposes, but also harbor works 
at least suitable to the vessels then in use. The marine activity 
of the Phoenicians is undoubted, and there is strong reason to 
believe that there was also similar activity between Babylonian 
ports and those east of them along the shores of the Indian 
Ocean, perhaps even as far as ancient Cathay, and possibly also 
to the eastern coast of Africa. 

Investigations in the early history of Egypt have .shown 
that a Phoenician fleet, constructed at some Egyptian port on 
the Red Sea, undoubtedly made the complete circuit of Africa 
and returned to Egypt through the Mediterranean Sea the third 
year after setting out, over 2100 years (about 600 B.C.) before 
the historic fleet of the Portuguese explorer Vasco da Gama 
sailed the same circuit in the opposite direction. It is therefore 
probable, in view of these facts, that at least simple harbor works 
of sufficient efficiency for those early days found place in the 
public works of the ancient kingdoms bordering upon the Medi- 
ten-anean and Red seas and the Persian Gulf. 



8 ANCIENT CIVIL-ENGINEERING WORKS. 

5. The Change of the Nile Channel at Memphis. — iVlthough 
such obscure accounts as can be gathered in connection with the 
founding of the city of Memphis are so shadowy as to be largely 
legendary, it has been established beyond much if any doubt 
that prior to its building the reigning Egyptian monarch deter- 
mined to change the course of the Nile so as to make it flow on 
the easterly side of the valley instead of the westerly. This was 
for the purpose of securing ample space for his city on the west of 
the river, and, also, that the latter might furnish a defence 
towards the east, from which direction invading enemies usually 
approached. He accordingly formed an immense dam or dike 
across the Nile as it then existed, and compelled it to change 
its course near the foot of the Libyan Hills on the west 
and seek a new channel nearer the eavSterly side of the valley. 
This must have been an engineering work of almost appalling 
magnitude in those early times, yet even with the crude means 
and limited resources of that early period, possibly, if not proba- 
bly, at least 5000 b.c, the work was successfully accomplished. 

6. The Pyramids. — Among the most prominent ancient 
structural works are the pyramids of Egypt, those royal tombs 
of which so much has been written. These are found chiefly 
in the immediate vicinity of Memphis on the Nile. There are 
sixty or seventy of them in all, the first of which was built by 
the Egyptian king Khufu and is known as the ' ' Great Pyramid ' ' 
or the ' ' First Pyramid of Ghizeh." They have been called ' ' the 
most prodigious of all human constructions." Their ages are 
uncertain, but they probably date from about 4000 B.C. to about 
2500 B.C. These are antedated, however, by two Egyptian 
pyramidal constructions of still more ancient character whose 
ages cannot be determined, one at Meydoum and the other at 
Saccarah. 

The pyramids at Memphis are constructed of limestone and 
granite, the latter being the prominent material and used entirely 
for certain portions of the pyramids where the stone would be 
subjected to severe duty. The great mass of most of the pyra- 
mids consists of roughly hewn or squared blocks with little of 
any material properly considered mortar. The interior portions, 
especially of the later pyramids, were sometimes partially com- 



THE PYRAMIDS. 



posed of chips, rough stones, mud bricks, or even mud, cellular 
retaining- walls being used in the latter cases for the main struc- 




A Corner of the Great Pyramid. 
(Copyright by S. S. McClure Co., 1902. Courtesy of McC2ure''s Magazine.) 

tural features. In all pyramids, however, the outer or exposed 
surfaces and the walls and roofs of all interior chambers were 
finished with finely jointed large stones, perhaps usually polished. 



10 



ANCIENT CIVIL-ENGINEERING WORKS. 




Fig. 2. — Section of the Great Pyramid. 



The Great Pyramid has a square base, which was originally 764 

feet on a side, with a height of apex above the surface of the 

ground of over 480 feet. This great mass of masonry contains 

about 3,500,000 cubic yards 
and weighs nearly 7,000,000 
tons. The area of its base 
is 13.4 acres. The Greek 
historian Herodotus states 
that its construction re- 
quired the labor of 100,000 
men for twenty years. An 
enormous quantity of gran- 
ite was required to be trans- 
ported about 500 miles down 
the Nile from the quarries at 

Syene. Some of the blocks at the base are 30 feet long with a 

cross-section of 5 feet by 4 or 5 feet. The bulk of the entire mass 

is of comparatively small 

stones, although so squared 

and dressed as to fit closely 

together. Familiar descrip- 
tions of this work have told 

us that the small passages 

leading from the exterior to 

the sepulchral chambers are 

placed nearly in a vertical 

plane through the apex. The 

highest or king's chamber, 

as it is called, measures 34 

feet by 17 feet and is 19 feet 

high, and in it is placed the 

sarcophagus of King Khufu. 

It is composed entirely of 

granite most exactly cut and 

fitted and beautifully polished. 




KING'S CHAMBER AND CHAMBERS 

OF CONSTRUCTION 

GREAT PYRAMID. 



Fig. 3. 
The construction of the roof is 
remarkable, as it is composed of nine great blocks ' ' each nearly 
19 feet long and 4 feet wide, which are laid side by side upon the 
walls so as to form a complete ceiling. ' ' There is a singular feature 



THE PYRAMIDS. 



11 



of construction of this ceiling designed to remove all pressure 
from it and consisting of five alternate open spaces and blocks 
of granite placed in vertical series, the highest open space being 




Entrance to the Great Pyramid. 



roofed over with inclined granite slabs leaning or strutted against 
each other like the letter V inverted. This arrangement relieves 
the ceiling of the sepulchral chamber from all pressure ; indeed 



12 ANCIENT CIVIL-ENGINEERING WORKS. 

only the inclined highest set of granite blocks or slabs carry any 
load besides their own weight. There are two small ventilating- 
or air-shafts running in about equally inclined directions upward 
from the king's chamber to the north and south faces of the pyra- 
mid. These air-shafts are square and vary between 6 and 9 
inches on a side. The age of this pyramid is probably not far 
from 5000 years. 

The second pyramid is not much inferior in size to the Great 
Pyramid, its base being a square of about 707 feet on a side, and 
its height about 454 feet. The remaining pyramids are much 
inferior in size, diminishing to comparatively small dimensions, 
and of materials much inferior to those used in the earlier and 
larger pyramids, 

7. Obelisks, Labyrinths, and Temples. — Among other con- 
structions of the Egyptians which may be called engineering in 
character, as well as architectural, are the obelisks, the ' ' Laby- 
rinth" so called, on the shore of Lake Moeris, and the magnificent 
temples at the ancient capital Thebes, which are the most remark- 
able architectural creations probably that the world has ever 
known. These latter were not completed by one king, as was 
each of the pyramids. They were sometimes despoiled and 
largely wrecked by invading hosts from Assyria, and then recon- 
structed in following periods by successive Egyptian kings and 
again added to by still subsequent monarchs, whose reigns were 
characterized by statesmanship, success in war, and prosperity 
in the country. Their construction conclusively indicates 
laborious operations and transportation of great blocks of stone 
characteristic of engineering development of the highest order 
for the days in which they took place. The dates of th^se con- 
structions are by no means well defined, but they extend over 
the period running from probably about 2500 B.C. to about 
400 B.C., with the summit of excellence abou.t midway between. 

Another class of ancient structures which can receive but a 
passing notice, although it deserves more, is the elaborate rock 
tombs of some of the old Egyptian monarchs in the rocks of the 
Libyan Hills. They were very extensive constructions and 
contained numerous successions of ' ' passages, chambers, cor- 
ridors, staircases, and pillared halls, each further removed from 



NILE IRRIGATION. 



13 



the entrance than the last, and all covered with an infinite number 
of brilliant paintings." These tombs really constituted rock 
tunnels with complicated ramifications which must have added 
miich to the difficulty of the work and required the exercise of 
engineering skill and resources of a high order. 

8. Nile Irrigation. — The value of the waters of the Nile for 
irrigation and fertilization were fully appreciated by the ancient 
Egyptians. They also apparently realized the national value 
of some means of equalizing the overflow, although the annual 
regimen of the Nile was unusually uniform. There were, however. 




MAP Of THC FAYOVm 

9MOWIN0 THE B/ RHET-EL- /f£/tOOI 

^ ND THE 

AHTIFICIAL LAKE 'M(B/f/3^ 



periods of great depression throughout the whole Nile valley 
consequent upon the phenomenal failure of overflow to the nor- 
mal extent. One of the earliest monarchs who was actuated by 
a fine pubHc spirit undertook to solve the problem of providing 
against such depressions by diverting a portion of the flood-waters 
of the Nile into an enormous reservoir, so that during seasons 
of insufficient inundation the reservoir-waters could be draw^n 
upon for the purpose of irrigation. This monarch is known as 
the good Amenemhat, although the Greeks call him Moeris. In 



14 ANCIENT CIVIL-ENGINEERING WORKS. 

the Nile valley, less than a hundred miles above Memphis, on 
the left side or to the west of the river, there is a gap in the Libyan 
Hills leading to an immense depression, the lower parts of which 
are much below the level of the water in the Nile. This topo- 
graphical depression, perhaps 50 miles in length by 30 in breadth, 
with an area between 600 and 700 square miles, now contains 
two bodies of water or lakes, one known as the Birket Keroun and 
the other as Lake Moeris. The vicinity of this depression is 
called the Fayoum. A narrow rocky gorge connects it with the 
west branch of the Nile, known as Bahr el Yousuf , and it is proba- 
ble that during extreme high water in the Nile there was a natural 
overflow into the Fayoum. The good Amenemhat, with the 
judgment of an engineer, or guided by advisers who possessed that 
judgment, appreciated the potential value of this natural depres- 
sion as a possible reservoir for the surplus Nile waters and exca- 
vated a channel, possibly a natural channel enlarged, of suitable 
depth from it to the Bahr el Yousuf. As a consequence he 
secured a storage-reservoir of enormous capacity and which 
proved of inestimable value to the lowlands along the Nile in 
times of shortage in the river -floods. 

Investigators have differed much in their conclusions as to 
the extent of this reservoir. Some have maintained that only 
the lower depressions of the Fayoum were filled for reservoir 
purposes, while others, like Mr. Cope Whitehouse, believe that 
the entire depression of the Fayoum was utilized with the excep- 
tion of a few very high points, and that the depth of water miight 
have been as much as 300 feet in some places. In the latter case 
the circuit of the lake would have been from 300 to 500 miles. 
Whatever may have been the size of the lake, however, its 
construction and use with its regulating-works was a piece of 
hydraulic engineering of the highest type, and it indicates an 
extraordinary development of that class of operations for the 
period in which it was executed. The exact date of this con- 
struction cannot be determined, but it may have been as early as 
2000 B.C., or perhaps earlier. 

9. Prehistoric Bridge-building. — The development of the 
art of bridge -building seems to have lagged somewhat in the 
prehistoric period. The use of rafts and boats prevented the 



ANCIENT BRICK-MAKING. 15 

need of bridges for crossing streams from being pressing. It 
is not improbable that some small and crude pile or other timber 
structures of short spans were employed, but no remains of this 
class of construction have been found. Large quantities of 
timber and much of an excellent quality were used in the con- 
struction of buildings. That much is known, but there is prac- 
tically no evidence leading to the belief that timber bridges of 
any magnitude were used by prehistoric people. It is highly 
probable that single -timber-beam crossings of small streams were 
used, but that must be considered the limit of ancient bridging 
until other evidence than that now available is found. 

10. Ancient Brick-making. — It has already been seen that 
stone as a building material has been used since the most ancient 
periods, and the use of brick goes back almost as far. Fortunately 
it w^as frequently a custom of the ancient brick-makers to stamp 
proprietary marks upon their bricks, and we know by these 
marks that bricks were made in the Chaldean regions certainly 
from 3000 to 4000 years before the Christian era. In Egypt 
also the manufacture of brick dates back nearly or quite as far. 
Some of these Chaldean bricks, as well as those in other parts of 
the ancient world, were of poor quality, readily destroyed by 
water or even a heavy storm of rain when driving upon them. 
Other bricks, however, were manufactured of good quality of 
material and by such methods as to produce results which com- 
pare favorably with our modern building-bricks. The ruins 
of cities, at least in Assyria and Chaldea, show that enormous 
buildings, many of them palaces of kings, were constructed 
largely of these bricks, although they were elaborately decorated 
with other material. The walls were heavy, indeed so massive 
that many of the ruin-mounds are frequently formed almost 
entirely of the disintegrated brick of poorer quality. These 
old builders not only executed their work on a large scale, but 
did not hesitate to pile up practically an artificial mountain of 
earth, or other suitable material, on which to construct a palace 
or temple. The danger of water to these native bricks was so 
well known and recognized that elaborate and very excellent 
systems of subsurface drains or sewers were frequently con- 
structed to carry off the storm-water as fast as it fell. 



16 ANCIENT CIVIL-ENGINEERING WORKS. 

II. Ancient Arches. — In the practice of these building 
operations it became necessary to form many openings and to 
construct roofs for the sewers or drains, and the arch, both true 
and false, came to be used in the Euphrates valley, in that of 
the Nile, and in other portions of the ancient world. Pointed 
sewer-arches of brick have been found in what is supposed to 
be the palace of Nimrod on the Tigris River, possibly of the 
date about 1300 b.c. Excavations at Nippur have revealed a 
mud-brick pointed arch supposed to date back to possibly 4000 
B.C. Also semicircular voussoir arches have been discovered 
at the ruins of Khorsabad near Nineveh with spans of 12 to 
15 feet. These arches are supposed to belong to the reign of 
Sargon, an Assyrian king who flourished about 705 to 722 B.C. 
Again, the ancient so-called treasury of Atreus at Mycenae in 
Greece, although a dome, exhibits an excellent examiple of the 
method of forming the false arch, the date of the construction 
being probably about 1000 b.c. The main portion of this struc- 
ture consists of a pointed dome, the diameter of the base being 





VAULTED DRAIN, KHORSABAD VAULTED DRAINS, KHO SABAa 

Fig. 4 Fig.. 5. 

48 feet and the interior central height 49 feet. A central section 
shows a beehive shape, as in Fig. 6. 

The exterior approach is between two walls 20 feet apart, the 
intermediate entrance to the dome or main chamber being a 
passage 9 feet 6 inches wide at the bottom and 7 feet 10 inches 
at the top and about 19 feet high. At right angles to the en- 
trance there is a chamber 27 feet by 20 feet cut into the adjacent 



ANCIENT ARCHES. 



17 



rock, entered through a doorway about 4 feet 6 inches wide and 
9 feet 6 inches high. Both the main entrance to the dome and 
the doorway to the adjacent chamber are covered or roofed 
with large flat hntel-stones, over which are the triangular reliev- 
ing (false) arches, so common in ancient construction, by which 
the lintels are relieved of load, the triangular openings being 
closed by single, great upright flat stones. There are a con- 
siderable number of these in Greece. The stone used is a " hard 





Fig. 6. — Plan and Section of the Treasury of Atreus at Mycenae. 

1. Plan of the Treasury of Atreus: A, rock-cut chamber, probably a tomb; 

B, doorway; C, approach. 

2. Section of the above: B, doorway; C, approach filled up with earth; D, 

slope of the ground; £, wall on north side of approach ; /% lintel 
stone, weight 133 tons; G, door to rock-cut chamber. 



and beautiful breccia" from the neighboring hills and Mount 
Eubora near by. The courses of stone are about two feet 
thick and closely fitted without cement. 

The great majority, or perhaps all, of the Assyrian true arches, 
so far discovered, are formed of wedge-shaped bricks, most of them 



18 ANCIENT CIVIL-ENGINEERING WORKS. 

» 

being semicircular, although some are pointed, the span being 
not over about 1 5 feet. The most of the arches found at Nineveh 
and Babylon belong to a period reaching possibly from 1300 to 
800 B.C., but some of the Egyptian arches are still older. Egyp- 
tians, Assyrians, Greeks, and other ancient people used false 
arches formed by projecting each horizontal course of stones 
or bricks over that below it on either side of an opening. 
The repetition of this procedure at last brings both sides of the 
opening together at the top of the arch, and they are surmounted 
at that point with a single flat stone, brick, or tile. It has been 
supposed by some that these false arches, whose sides may be 
formed either straight or curved, exhibit the oldest form of the 
arch, and that the true arch with its ring or rings of wedge- 
shaped voussoirs was a subsequent development. It is possible 
that this is true, but the complete proof certainly is lacking. 
In Egypt and Chaldea both styles of arches were used concur- 
rently, and it is probably impossible to determine which preceded 
the other. Again, some engineers have contended that two 
flat slabs of stone leaning against each other, each inclined like 
the rafters of a roof, was the original form of the arch, as found 
in the pyramids of Egypt ; but it is probable that the true arch 
was used in Chaldea prior to the time of the pyramids. Indeed 
crude arches of brick have been found at Thebes in Egypt dating 
back possibly to 2500 b.c, or still earHer. Aside from that, 
however, such an arrangement of two stones is not an arch at 
all, either true or false. The arrangement is simply a com- 
bination of two beams. A condition of stress characteristic of 
that in the true arch is lacking. 

The ancient character of the engineering works whose ruins 
are found in Chaldea and Assyria is shown by the simple facts 
that Babylon was destroyed about the year 690 b.c. and Nineveh 
about the year 606 b.c. 



CHAPTER II. 

12. The Beginnings of Engineering Works of Record. — In a 

later period of the world's history we reach a stage in the devel- 
opment of engineering works of which we have both records 
and remains in such well-defined shape that the characteristics 
of the profession may be realized in a definite manner. This is 
particularly true of the civil -engineering works of the Romans, 
In their sturdy and unyielding character, with their limitless 
energy and resolution, the conditions requisite for the execution 
of engineering works of great magnitude are found. An effemi- 
nate or generally aesthetic nation like the Greeks would furnish 
but indifferent opportunity for the inception and development 
of great engineering works, but the resolute and vigorous Roman 
nation offered precisely the conditions needed. They appre- 
ciated among other things the absolute necessityof the freest pos- 
sible communication with the countries which they conquered 
and made part of their own empire. They recognized water 
transportation as the most economical and effective, and used it 
wherever possible. They also realized the advantages of roads 
of the highest degree of solidity and excellence. No other roads 
have ever been constructed so direct, so solid, and so admirably 
adapted to their purposes as those built by the Romans. They 
virtually ignored all obstacles and built their highways in the 
most direct line practicable, making deep cuts and fills with 
apparently little regard for those features which we consider 
obstacles of sufficient magnitude to be avoided. They regarded 
this system of land communication so highly that they made it 
radiate from the Golden Mile-stone in the Roman Forum. The 
point from which radiated these roads was therefore in the very 
centre of Roman life and authority, and it fitly indicated the 
importance which the Roman government gave to the system 

19 



20 



ANCIENT CIVIL-ENGINEERING WORKS. 



of communication that bound together with the strongest bonds 
all parts of the republic and of the empire. 

The design and construction of these roads must have been 
a matter to which their constructors gave the most careful atten- 
tion and study. They were works involving principles deduced 
from the most careful thought and extended experience. There 
were incorporated in them the most effective materials of con- 
struction then known, and it was evidently the purpose of their 
constructors that they should possess indefinite endurance. The 
existence of some of them at the present time, with no other 
attention given to them than required for ordinary maintenance, 
demonstrates that the confidence of the builders was not mis- 
placed. 




Street Fountain and Watering-trough in Pompeii. Called the Fountain of Plenty, from 
the figure with Horn of Plenty on the perforated upright post. 

13, The Appian Way and other Roman Roads. — Probably the 
oldest and most celebrated of these old Roman roads is the Appian 
Way. It was the most substantially built, and the breadth of 
roadway varied from 14 to 18 feet exclusive of the footwalks. 
Statius called it the Queen of Roads. It was begun by Appius 
Claudius Cascus, 312 years before the Christian era. He carried 



THE A P PI AN WAY AND OTHER ROMAN ROADS. 31 

its construction from the Roman gate called Porta Capena to 
Capua, but it was not entirely completed till about the year 
30 B.C. Its total length was three hundred and fifty miles, and 
it formed a perfect highway from Rome to Brundisium, an 
important port on what may be called the southeastern point 
of Italy, It was built in such an enduring manner that it appears 
to have been in perfect repair as late as 500 to 565 a.d. 

The plan of construction of these roads was so varied as to 
suit local conditions, but only as required by sound engineering 
judgment. They wisely employed local materials wherever 
possible, but did not hesitate to transport proper material from 
distant points wherever necessary. This seemed to be one of 
their fundamental principles of road construction. In this 
respect the old Romans exhibited more engineering and business 
wisdom than some of the American states in the beginnings of 
improved road construction in this country. An examination 
of the remains of some Roman roads now existing appears to 
indicate that in earth the bottom of the requisite excavation was 
first suitably compacted, apparently by ramming, although 
rollers may have been used. On this compacted subgrade were 
laid two or three courses of flat stones on their beds and generally 
in mortar. The second layer placed on the preceding was rubble 
masonry of small stones or of coarse concrete. On the latter 
was placed the third layer of finer concrete. The fourth or 
surface course, consisting of close and nicely jointed polygonal 
blocks, was then put in place, and formed an excellent unyielding 
pavement. This resulted in a most substantial roadway, some- 
times exceeding 3 feet in total thickness. It is difficult to con- 
ceive of a more substantial and enduring type of road construction. 
The two lower layers were omitted when the road was con- 
structed in rock. Obviously the finer concrete constituting the 
second layer from the top surface was a binder between the 
pavement surface and the foundation of the roadway structure. 

The paved part of a great road was usually about 16 feet in 
width, and raised stone causeways or walls separated it from an 
unpaved way on each side having half the width of the main 
or paved portion. This seemed to be the type of the great or 
main Roman roads. Other highways of less important character 



22 



ANCIENT CIVIL-ENGINEERING WORKS. 



=3'l(> 


^ 


^V 


3 




H 


- 


^^ 




5 10 Ft. 

EXAMPLE OF EARLY BASALT ROAD. 
BY THE TEMPLE OF SATURN 
ON THE CLIVUS CAPITOLINUS. 



Fig. 7- 



were constructed of inferior materials, earth or clay sometimes 
being used instead of mortar; but in such cases greater crown- 
ing was employed, and the road was 
more elevated, possibly for better drain- 
age. Then, as now, adequate drainage 
was considered one of the first features 
of good road design. City streets were 
paved with the nicely jointed polygonal 
blocks to which reference has already 
been made, while the footways were 
paved with rectangular slabs much like 
our modem sidewalks. 

The smooth polygonal pavements of 
the old Romans put to the keenest 
shame the barbarous cobblestone street 
surfaces with which the people of American cities have been 
and are still so tortured. 

The beneficial influence of these old Roman highways has 
extended down even to the present time in France, where some 
of them were built. The unnecessarily elaborate construction 
has not been followed, but the recognition of the pubHc bene- 
fits of excellent roads has been maintained. The lower course 
of the foundation-stones apparently began to be set on edge 
toward the latter part of the eighteenth century, the French 
engineer Tresaguet having adopted that practice in 1764. At 
the same time he reduced the thickness of the upper layers. His- 
methods were but modifications of the old Roman system, and 
they prevailed in France until the influence of the English engi- 
neers Macadam and Telford began to be felt. 

14. Natural Advantages of Rome in Structural Stones. — 
Although the ancient Romans were born engineers, possessing 
the mental qualities and sturdy character requisite for the analytic 
treatment and execution of engineering problems, it is doubtful 
whether they would have attained to such an advanced position 
in structural matters had not the city of Rome been so favorably 
located. 

The geological character of the great Roman plain and the 
Roman hills certainly contributed most materially to the early 



NATURAL ADVANTAGES OF ROME IN STRUCTURAL STONES. 23 

development of some of the most prominent of the Roman 
engineering works. The plain surrounding the city of Rome is 
composed largely of alluvial and sandy deposits, or of the emis- 
sions of neighboring volcanoes, of which the Alban Hills form a 
group. While these and other volcanic hills in the vicinity are, 
and have been for a long period, quiescent, they were formerly 
in a very active state. The scoriae, or matter emitted in volcanic 
eruptions, is found there in all possible degrees of coherence or 
solidity, from pulverulent masses to hard rock. The charac- 
teristic Roman material called tufa is a mixture of volcanic ash 
and sand, loose and friable, as dropped from the eruptions in 
large quantities or again compressed into masses with all degrees 
of hardness. The hard varieties of yellow or brown tufa form 
building material much used, although a considerable percentage 
of it would not be considered fit building material for structures 
of even moderate .height at the present time. The most of it 
weathers easily, but forms a fairly good building-stone when 
protected by a coating of plaster or stucco. 

Another class of building-stones found at or in the vicinity 
of Rome is the so-called ' ' peperino, ' ' consisting chiefly of two 
varieties of conglomerate of ash, gravel, broken pieces of lava, 
and pieces of limestone, some possessing good weathering quali- 
ties, while others do not. Ancient quarries of these stones exist 
whence millions of cubic yards have been removed, and are still 
being worked. The better varieties of ' 'peperino" possess good 
resisting qualities, and were much used in those portions of 
masonry construction where high resistance was needed, as in 
the ring-stones of arches, heavily loaded points of foundations, 
and other similar situations. 

Some of the prehistoric masonry remains of the Romans 
show that their earliest constructors appreciated intelligently 
the qualities of this stone for portions of works where the duty 
was most severe. 

Lava from the extinct volcanoes of the Alban Hills called 
"silex" was used for paving roads and for making concrete. 
It was hard and of gray color. At times considerable quantities 
of this stone were employed. A species of pure limestone called 
"travertine," of a creamy white color, was quarried at Tibur or 



24 ANCIENT CIVIL-ENGINEERING WORKS. 

Tivoli, and began to be used about the second century B.C. 
Vitruvius speaks of its having good weathering qualities, but 
naturally it is easily calcined. Its structure is crystalline, and 
it is strong in consequence of that quality only when it is laid on 
its bed. 

15. Pozzuolana Hydraulic Cement,— The most valuable of 
all building materials of old Rome was the "pozzuolana," as it 
furnished the basis of a strong, enduring, and economic con- 
crete, and permitted almost an indefinite development of masonry 
construction. Had there not been at Rome the materials ready 
at hand to be manufactured into an excellent cementing product, 
it is highty probable that neither the structural advance nor 
the commercial supremacy of the Roman people could have been 
attained. It is at least certain that the majority of the great 
masonry works constructed by the Romans could not have 
been built without the hydraulic cementing material produced 
with so little difficulty and in such large quantities from the 
volcanic earth called pozzuolana. The name is believed to have 
its origin from the large masses of this material at Pozzuoli near 
Naples. Great beds are also found at and near Rome. The 
earliest date of its use cannot be determined, but it has given 
that strong and durable character to Roman concrete which has 
enabled Roman masonry to stand throughout centuries, to the 
admiration of engineers. 

It is a volcanic ash, generally pulverulent, of a reddish color, 
but differs somewhat in appearance and texture according to 
the locality from which it is taken. It consists chiefly of silicate 
of alumina, but contains a little oxide of iron, alkali, and possibly 
other components. The Romans therefore pulverized the poz- 
zuolana and mixed it with lime to make hydraulic cement. This 
in turn was mixed with sand and gravel and broken stone to form 
mortar and concrete, and that process is carried on to this day. 
The concrete was hand-mixed, and treated about as it is at present. 
After having been well mixed the Romans frequently deposited 
it in layers of 6 to 9 or 10 inches thick, and subjected it to 
ramming. In connection with this matter of mortar and concrete 
production, \^itruvius observes that pit sand is preferable to 
Neither sea or river sand. 



ROMAN BRICKS AND MASONRY 35 

i6. Roman Bricks and Masonry. — The Romans produced 
bricks both by sun-baking and by burning, although there are 
now remaining apparently no specimens of the former in Rome. 
Bricks were used very largely for facing purposes, such as a 
veneer for concrete work. The failure to recognize this fact has 
led some investigators and writers into error. As matter of fact 
bricks were used as a covering for concrete work, the latter per- 
forming all the structural functions. 

The old Roman aqueducts were frequently lined with con- 
crete, made of a mixture of pozzuolana, lime, and crushed 
(pounded) bricks or potsherds. The same material was also 
used for floors under the fine mortar in which the mosaics were 
imbedded. 

Marble came into use in Rome about loo B.C., from Luna, 
near modern Carrara, Mt. Hymettus, and Mt. Pentelicus, near 
Athens and the Isl-e of Paros, nearly all being for sculpture 
purposes. Colored and structural marbles were brought from 
quarries in various parts of Italy, Greece, Phrygia, Egypt, 
near Thebes (oriental alabaster or "onyx"), Arabia, and near 
Damascus. 

From the latter part of the first century b.c. the hard building- 
stones like granites and basalts were brought to Rome in large 
quantities. Most of the granites came from Philae on the Nile. 
The basalts came both from Lacedasmonia and Egypt. Both 
emery (from the island of Naxos in the .-Egean Sea) and diamond- 
dust drills were used in quarrying or working these stones. 
Ships among the largest, if not the largest, of those days, were 
built to transport obelisks and other large monoliths. 

The quality of ancient Roman mortar varies considerably 
as it is now found. That of the first and second centuries is 
remarkably hard, and made with red pozzuolana. In the third 
century it began to be inferior in quality, brown pozzuolana 
sometimes being used. The reason for this difference in quality 
cannot be confidently assigned. The deterioration noted in the 
third-century work may be due to the introduction of bad ma- 
terials, or to the wrong manipulation of material intrinsically 
good, or it is not unlikely the deterioration is due to a combina- 
tion of these two influences. . The use of mortar indicates a class 



26 ANCIENT CIVIL-ENGINEERING WORKS. 

of early construction; it is found in the Servian wall on the 
Aventine, of date 700 b.c, or possibly earlier. 

Under the empire (27 b.c. to a.d. 475) large blocks of tufa, 





Dovetail Wooden Tenon. Wooden Dowel. 

Fig. 8. 

limestone (travertine), or marble were set with very close 
joints, with either no mortar or, if any, as thin as paper; end, 
top, and bottom clamps of iron were used to bond such stones 
together. It was also customary, in laying such large, nicely 
finished blocks of stone without mortar, to use double dove- 
tailed wooden ties, or, as in the case of columns, a continuous 
central dowel of wood, as shown in the figures. 

The joints were frequently so close as to give the impression 
that the stones might have been fitted by grinding together. 
In rectangular dimension stonework (ashlar) great care was 
taken, as at present, to secure a good bond by the use of judi- 
ciously proportioned headers and stretchers. Foundation courses 
were made thicker than the body of the superincumbent wall, 
apparently to distribute foundation weights precisely as done 
at present. Weaker stone was used in thicker portions of walls, 
and strong stone in thinner portions. Also at points of con- 
centrated loading, piers or columns of strong stone are found 
built into the bodies of walls of softer or weaker stone. Quarry 
chips, broken lava, broken bricks, or other suitable refuse frag- 
ments were used for concrete in the interest of economy, the 
broken material always being so chosen as to possess a sharp 
surface to which the cement would attach itself in the strongest 
possible bond. 

At the quarries where the stones were cut the latter were 
marked apparently to identify their places in the complete 



ROMAN BRICKS AND MASONRY 27 

structure, or for other purposes. The remains of the quarries 
themselves as seen at present are remarkable both for their 
enormous extent and for the system on which the quarrying 
was conducted. It appears that the systems employed were 
admirably adapted to the character of the stone worked, and 
that the quarrying operations were executed as efficiently and 
with as sound engineering judgment as those employed in great 
modem quarries. 

17. Roman Building Laws. — So much depended upon the 
excellence of the building in Rome, and upon the materials and 
methods employed, that building laws or municipal regulations 
were enacted in the ancient city, prescribing kind and quality 
of material, thickness of walls, maximum height of buildings, 
minimum width of streets, and many other provisions quite 
similar to those enacted in our modem cities. The differences 
appear to arise froin the different local conditions to be dealt 
with, rather than from any failure on the part of the old Romans 
to reach an adequate conception of the general plans suitable for 
the masses of buildings in a great city. Prior to the great fire 
A.D. 64 in Nero's reign, an act prescribing fire-proof exterior 
coverings of buildings was under consideration, and subsequently 
to that conflagration it was enacted into law. Many of the city 
roads or streets were paved with closely fitting irregular polyg- 
onal blocks of basalt, laid on concrete foundations, and with 
limestone (travertine) curbs and gutters, producing an effect 
not unlike our modern streets. 

18. Old Roman Walls. — In no class of works did the ancient 
Romans show greater engineering skill or development than in 
the massive masonry structures that were built not only in and 
about the city of Rome, but also in distant provinces under 
Roman jurisdiction. Among the home structures various walls, 
constituting strong defences against the attacks of enemies, stand 
in particular prominence. Some of these great structures had 
their origin prior even to historic times. The so-called "Wall 
of Romulus, " around the famous Roma Quadrata of the Palentine, 
is among the latter. It is supposed by many that this wall 
formed the primitive circuit of the legendary city of Romulus. 
That, however, is an archaeological and not an engineering ques- 



28 ANCIENT CIVIL-ENGINEERING WORKS. 

tion, and, whatever its correct answer may be, the wall itself is 
a great engineering work; it demonstrates that the early- 
Romans, whatever may have been their origin, had attained 
no little skill in quarrying and in the building of dry masonry, 
no mortar being used in this ancient wall. Portions of it 40 feet 
high and 10 feet thick at bottom, built against a rocky hill, are 
still standing. The courses are 22 to 24 inches thick, and they 
are laid as alternate headers and stretchers; the lengths of the 
blocks being 3 to 5 feet, and the width from 19 to 22 inches. The 
ends of the blocks are carefully worked and true, as are the verti- 
cal joints in much of the wall, although some of the latter, on 
the other hand, are left as much as 2 inches open. 

Civil engineers, who are familiar with the difficulties fre- 
quently experienced in laying up dry walls of considerable height, 
as evidenced by many instances of failure probably within the 
knowledge of every experienced engineer, will realize that this 
great dry -masonry structure must have been put in place by men 
of no little engineering capacity. The rock is soft tufa, and 
marks on the blocks indicate that chisels from i to | inch in 
width were used, as well as sharp-pointed picks. In all cases 
the faces of the blocks were left undressed, i.e., in modern terms 
they were "quarry -faced." 

19. The Servian Wall. — Later in the history of Rome the 
great Servian Wall, built chiefly by Servius Tullius to enclose the 
seven hills of Rome, occupies a most prominent position as an 
engineering work. Part of the wall, all of which belongs to the 
regal period (753 to 509 B.C.), is supposed to be earlier than 
Servius, and may have been planned and executed by Tarquinius 
Priscus. A part only of the stones of this wall were laid in 
cement mortar, and concrete was used, to some extent at least, 
in its foundation and backing. The presence of cement mortar 
in this structure differentiates it radically from the wall of Rom- 
ulus. Probably the discovery of pozzuolana cement, and the 
fabrication of mortar and concrete from it, had been made in the 
intervening period between the two constructions. Tufa, 
usually the softer varieties but of varying degrees of hardness, 
was mostly used in this wall, and the blocks were placed, as in 
the previous instance, as alternate headers and stretchers in 



OLD ROMAN SEWERS. 



29 



courses about two feet thick. Portions of the wall 45 feet high 
and about 12 feet thick have been uncovered. At points it was 
pierced with arched openings of 11 feet 5 inches span, possibly 
as embrasures for catapults or other engines of war. The upper 
parts of these openings are circular arches with the usual 
wedge-like ring-stones. The voussoirs were cut from peperino 
stone. This wall, like that of Romulus, was constructed as 
a military work of defence, and at some points it was built up 




«PfipW F-f 



STE 



PLAN OF WALL*"'""' ^''>"^ "'^^ Agger 



SCALE OF SECTION 



^ 



Fig. 9. — Part of Servian Wall 
on Aventine. 







Y/////.^/^m'w/y wj^^;;;;;,;,;;,;^/,^ ^^ii2^^^ 



Fig. 10. — Wall and Agger 

of Servius. 



from the bottom of a wide foss 30 feet deep. At such places 
it was counterforted or buttressed, a portion of wall 11 feet 
6 inches long being found between two counterforts, each of 
the latter being 9 feet wide and projecting 7 feet 9 inches out 
fjom the wall. 

20. Old Roman Sewers. — It is demonstrable by the writings 
of Vitruvius and others that the old Romans, or at any rate the 
better educated of them, possessed a correct general idea of some 
portions of the science of Sanitary Engineering, so far as any- 
thing of the nature of science could then be known. Their sani- 
tary views were certainly abreast of the scientific knowledge of 
that early day. The existence of the ' ' cloacae, " or great sewers, 
of the ancient city of Rome showed that its people, or at least its 
rulers, not only appreciated the value of draining and sewering 
their city, but also that they knew how to secure the construction 
of efficient and enduring sewers or drains. It has been stated, and 
it is probably true, that this system of cloacae, or sewers, was so 
complete that every street of the ancient city was drained through 



30 ANCIENT CIVIL-ENGINEERING WORKS. 

its members into the Tiber. They were undoubtedly the result 
of a gradual growth in sewer construction and did not spring at 
once into existence, but they date back certainly to the beginning 
of the period of the kings (753 B.C.). The famous Cloaca Max- 
ima, as great as any sewer in the system, and certainly the most 
noted, is still in use, much of it being in good order. The mouth 
of the latter where it discharges into the Tiber is 11 feet wide 
and 12 feet high, constituting a large arch opening with three 
rings of voussoirs of peperino stone. Many other sewers of this 
system are also built with arch tops of the same stone, with 
neatly cut and closely fitting voussoirs. We do not find, unfor- 
tunately, any detailed accounts of the procedures involved in the 
design of these sewers, yet it is altogether probable that the old 
Roman civil engineers formed the cross-sections, grades, and 
other physical features of their sewer system by rational processes, 
although they would doubtless appear crude and elementary at 
the present time. It would not be strange if they made many 
failures in the course of their structural experiences, but they 
certainly left in the old Roman, sewers examples of enduring 
work of its kind. 

Some portions of this ancient sewer system are built with 
tops that are not true arches, and it is not impossible that they 
antedate the regal period. These tops are false arches formed 
of horizontal courses of tufa or peperino, each projecting over 
that below until the two sides thus formed meet at the top. The 
outline of the crowns of such sewers may therefore be triangular, 
curved, or polygonal; they were usually triangular. Smaller 
drains forming feeders to the larger members of the system were 
formed with tops composed of two flat stones laid with equal 
inclination to a vertical line so as to lean against each other at 
their upper edges and over the axis of the sewer. This method 
of forming the tops of the drains by two inclined flat stones was 
a crude but effective way of accomplishing the desired purpose. 

The main members of this great sewer system seem to have 
followed the meandering courses of small rivers or streams, con- 
stituting the natural drainage-courses of the site of the city. The 
Cloaca Maxima has an exceedingly crooked course and it, along 
with others, was probably first formed by walling up the sides 



EARLY ROMAN BRIDGES. 31 

of a stream and subsequently closing in the top. Modern engi- 
neers know that such an alignment for a sewer is viciously bad, 
and while this complicated system of drains is admirably con- 
structed in many ways for its date, it cannot be considered a 
perfect piece of engineering work in the light of present engineer- 
ing knowledge. It is probable that the walling in of the sides of 
the original streams began to be done in Rome at least as early 
as the advent of the Tarquins, possibly as early as 800 b.c. or 
earlier. 

We know little about the original outfalls or points of dis- 
charge into the Tiber, except that, as previously stated, these 
points were made through the massive quay -walls constructed 
during the period of the kings along both shores of the Tiber, 
probably largely for defence as originally built. The discharge 
of the old Roman sewers through the face of this quay-wall and 
into the river is precisely the manner in which the sewers of New 
York City in many places are discharged into the North, East, 
and Harlem rivers. 

The Cloaca Maxima is not the only great ancient sewer thus 
far discovered. There are at least two others equal to it, and 
some of the single stones with which they are built contain as 
much as 45 cubic feet each. These cloacae were not mere sewers; 
indeed they were more drains than sewers, for they carried off 
flood-waters and the natural drainage as well as the sewer- 
age. They were therefore combined sewers and drains closely 
akin to the sewers of our ' ' combined ' ' systems. The openings into 
them were made along the streets of Rome and in public build- 
ings or some other public places. There is no evidence that they 
were ventilated except through these openings, and from each 
noxious gases were constantly rising to be taken into the lungs of 
the passers-by. It is a rather curious as well as important fact 
that so far as excavations have been made there is practically no 
evidence that a private residence in Rome was connected with 
the sewers. The "latrines" were generally located adjacent 
to the Roman kitchens and discharged into the cloacae. 

21. Early Roman Bridges. — The early Romans were excellent 
bridge -builders as well as constructors in other lines of engineering 
work. Although the ancient city was first located on the left 



33 ANCIENT CIVIL-ENGINEERING WORKS. 

bank of the Tiber, apparently it was but a comparatively short 
time before the need of means for readily crossing from bank to 
bank was felt. The capacity of the Roman engineers was equal 
to the demands of the occasion, and it is now known that seven or 
eight ancient bridges connected the two shores of the river Tiber. 
The oldest bridge is that known as Pons Sublicius. No iron was 
used in its construction, as bronze was the chief metal employed 
in that early day. The structure was probably all of timber 
except possibly the abutments and the piers. A French engi- 
neer, Colonel Emy, has exhibited in his ' ' Traite de I'Art de la 
Charpenterie ' ' a plan of this structure restored as an all-timber 
bridge with pile foundations. Lanciani, on the other hand, be- 
lieves that the abutments and piers must have been of masonry. 
The masonry structures, however, known to exist at a later day 
may have been parts of the work of rebuilding after the two 
destructions by floods. The date of its construction is not 
known, but tradition places it in the time of Ancus Marcius. 
This may or may not be correct. A flood destroyed the bridge 
in 23 B.C., and again in the time of Antoninus Pius, but on both 
occasions it was rebuilt. The structure has long since disap- 
peared. The piers only remained for a number of centuries, and 
the last traces of them were removed in 1877 in order to clear 
the bed of the river. 

Fig. II shows Colonel Emy's restoration of the plan for the 
pile bridge which Julius Csesar built across the Rhine in ten days 
for military purposes. This plan may or may not include accu- 
rate features of the structure, but it is certain that such a timber 
bridge was built, and well preserved pieces of the piles have been 
taken from under water at the site little the worse for wear after 
two thousand years of submersion. 

The censor ^Elius Scaurus built a masonry arch across the 
Tiber about a mile and a half from Rome in the year 100 b.c. 
This bridge is now known as the Ponte Molle, and some parts 
of the original structure are supposed to be included in it, having 
been retained in the repeated alterations. The arches vary in 
span from 51 to 79 feet, and the width of the structure is a little 
less than 29 feet. 

In or about the year 104 a. d. the emperor Trajan constructed 



EARLY ROMAN BRIDGES. 



33 



what is supposed to be a wooden arch bridge with masonry piers 
across the Danube just below the rapids of the Iron Gate. 

A bas relief on the Trajan Column at Rome exhibits the tim- 
ber arches, but fails to give the span lengths, which have been the 




Plan at Pie 



Fig. II. — Bridge thrown across the Rhine by Julius Ccesar. 

subject of much controversy, some supposing them to have been 
as much as 170 feet. 

The ancient Pons Fabricius, now known as Ponte Quattiro 
Capi, still exists, and it is the only one which remains intact after 
an expiration of nearly two thousand years. It has three arches, 
the fourth being concealed by the modern embankment at one end ; 
a small arch pierces the pier between the other two arches. This 
structure is divided into two parts by the island of ^Esculapius. 
It is known that a wooden bridge must have joined that island 
with the left bank of the Tiber as early as 192 b.c, and a similar 
structure on the other side of the island is supposed to have 
completed the structure. While Lucius Fabricius was Commis- 
sioner of Roads in the year 62 b.c. he reconstructed the first- 
named portion into a masonry structure of arches. An engraved 
inscription below the parapets shows that the work was duly and 
satisfactorily completed, and further that it was the custom to 
require the constructors or builders of bridges to guarantee their 
work for the period of forty years. Possession of the last deposit,. 



34 



ANCIENT CIVIL-ENGINEERING WORKS. 



made in advance as a guarantee of the satisfactory fulfilment of 
the contract, could not be regained until the forty -first year after 
completion. 

The Pons Cestius is a bridge since known as the Pons Gra- 
tianus and Ponte di S. Bartolomeo. Its first construction is 




Fig. 12. — Trajan's Bridge. 

supposed to have been completed in or about 46 b.c, and it was 
rebuilt for the first time in a. d. 365. A third restoration took 
place in the eleventh century. The modern reconstruction in 
1886-89 was so complete that only the middle arch remains as 
an ancient portion of the structure. The island divides the 
bridge into two parts, the Ship of ^sculapius lying between the 
two, but it is not known when or by whom the island was turned 
into that form. 

Another old Roman bridge, of w^hich but a small portion is 
now standing, is Pons .^milius, the piers of which were founded 
in 181 B.C., but the arches were added and the bridge completed 
only in 143 B.C. It was badly placed, so that the current of the 
river in times of high water exerted a heavy pressure upon the 
piers, and in consequence it was at least four times carried away 
by floods, the first time in the 3^ear a.d. 280. 

The discovery of what appears to be a row of three or four 
ruins of piers nearly 340 feet up-stream from the Ponte Sisto 
seems to indicate that a bridge was once located at that point, 
although little or nothing is known of it as a bridge structure. 
Some suppose it to be the bridge of Agrippa. 

The most historical of all the old Roman bridges is that which 
was called Pons ^lius, now known as Ponte S. Angelo, built by 
Hadrian a.d. 136. Before the reconstruction of the bridge in 



BRIDGE OF ALCANTARA. 35 

1892 six masonry arches were visible, and the discovery of two 
more since that date makes a total of eight, of which it is supposed 
that only three were needed in a dry season. The pavement of 
the approach to this bridge as it existed in 1892 was the ancient 
roadway surface. Its condition at that time was an evidence of 
the substantial character of the old Roman pavement. 

Below the latter bridge remains of another can be seen at 
low water. It is supposed that this structure was the work of 
Nero, although its name is not known. 

The modern Ponte Sisto is a reconstruction of the old Pons 
Valentinianus or bridge of Valentinian I. The latter was an old 
Roman bridge, and it was regarded as one of the most impressive 
of all the structures crossing the river. It was rebuilt in a.d. 
366-67. 

The most of these bridges were built of masonry and are of 
the usual substantiah type characteristic of the early Romans. 
They were ornamented by masonry features in the main portions 
and by ornate balustrades along either side of the roadway and 
sidewalks. The roadway pavements were of the usual irregular 
polygonal old Roman type, the sidewalk surfaces being com- 
posed of the large slabs or stones commonly used in the early 
days of Rome for that purpose. 

22. Bridge of Alcantara. — Among the old Roman bridges 
should be mentioned that constructed at Alcantara in Spain, 
supposedly by Trajan, about a.d. 105. It is 670 feet long and 
its greatest height is 210 feet. One of its spans is partially de- 
stroyed. The structure is built of blocks of stone without 
cementing material. In this case the number of arches is even, 
there being six in all, the central two having larger spans than 
those which flank them. It is a bridge of no little impressiveness 
and beauty and is a most successful design. 

23. Military Bridges of the Romans. — In the old Roman mili- 
tary expeditions the art of constructing temporary timber struc- 
tures along lines of communication was well known and practised 
with a high degree of ability. Just what system of construction 
was employed cannot be determined, but piles were constantly 
used. At least some of these timber military bridges, and possi- 
bly all, were constructed with comparatively short spans, the 



36 ANCIENT CIVIL-ENGINEERING WORKS. 

trusses being composed of such braces and beams as might be 
put in place between bents of piles. As already observed, some 
of the sticks of these bridges have been found in the beds of 
German rivers, and at other places, perfectly preserved after 
an immersion of about two thousand years. These instances 
furnish conclusive evidence of the enduring qualities of timber 
always saturated with water. 

24. The Roman Arch. — The Romans developed the semicir- 
cular arch to a high degree of excellence, and used it most exten- 
sively in many sewers, roads, and aqueducts. While the aque- 
duct spans were usually made with a length of about 18 or 20 
feet, they built arches with span lengths as much as 120 feet or 
more, comparing favorably with our modern arch-bridge work. 
They seldom used any other curve for their arches than the cir- 
cular, and when they built bridges an odd number of spans was 
usually employed, with the central opening the largest, possibly 
in obedience to the well-known esthetic law that an odd number 
of openings is more agreeable to the eye than an even number. 
Apparently they were apprehensive of the safety of the piers 
from which their arches sprang, and it was not an uncommon 
rule to make the thickness of the piers one third of the clear span. 
Nearly one fourth of the entire length of the structure would thus 
be occupied by the pier thicknesses. Although the use of mortar, 
both lime and cement, early came into use with the Romans, 
they usually laid up the ring-stones of their arches dry, i.e., with 
out the interposition of mortar joints. 



CHAPTER III. 

25. The Roman Water-supply. — There is no stronger evidence 
of engineering development in ancient Rome, nor of the ad- 
vanced state of civilization which characterized its people, than 
its famous system of water-supply, which was remarkable both 
for the volume of water daily supplied to the city and for ^ the 
extensive aqueducts, many of whose ruins still stand, as impres- 
sive monuments of the vast public works completed by the 
Romans. These ruins, and those of many other works, would 
of themselves assure, us of the elaborate system of supply, but 
fortunately there has been preserved a most admirable descrip- 
tion of it, the laws regulating consumption, the manner of ad- 
ministering the water department of the government of the 
ancient city, and much other collateral information of a most 
interesting character. In the work entitled, in English, "The 
Two Books on the Water-supply of the City of Rome," by 
(Sextus) Julius Frontinus, an eminent old Roman citizen, who, 
besides having filled the office of water commissioner * of the 
city, was governor of Britain and three times consul, as well as 
having enjoyed the dignity of being augur. He may properly 
be called a Roman engineer, although he evidently was a man 
of many public affairs, and so esteemed by the emperors who 
ruled during his time that he accompanied them in various wars 
as a mihtary man of high rank. He wrote seven books at least, 
viz., "A Treatise on Surveying, "" Art of War," " Strategemat- 
ics," "Essays on Farming," "Treatise on Boundaries, Roads, 
etc.," "A Work on Roman Colonies," and his account of the 
water- works of Rome, entitled "De Aquis." It is the latter 

* The first permanent water commissioner in Rome was M. Agrippa, son-in-law of 
Csesar Augustus, who took office B.C. 34. He was one of the greatest Roman engineers 
and constructors, if indeed he was not the first in rank. 

37 



38 ANCIENT CIVIL-ENGINEERING WORKS. 

book in which engineers are particularly interested. The trans- 
lation of this book from the original Latin is made from what is 
termed the " Montecassino Manuscript," an account of which 
with the translation is given by Mr. Clemens Herschel in his en- 
tertaining work, ' ' Frontinus, and the Water-supply of the City 
of Rome." 

As near as can be determined Frontinus lived from about 
A.D. 35 to A.D. 103 or 104. Judging from the offices which Fronti- 
nus held and the honors which he enjoyed throughout his life, it 
would appear that he was a patrician; he was certainly a man 
of excellent executive capacity, of intellectual vigor and refined 
taste, and a conscientious public servant. The water-supply 
of the city was held by the Romans to be one of the most impor- 
tant of all its public works, and its administration during the life 
of Frontinus was entrusted to what we should call a water 
commissioner, appointed by the emperor. It was considered 
to be an office of dignity and honor, and the proper discharge of 
its responsibilities was a public duty which required a high order 
of talent, as well as great integrity of character. 

26. The Roman Aqueducts. — Frontinus states that from the 
foundation of the city of Rome until 313 B.C., i.e., for a period 
of 441 years, the only water-supply was that drawn either from 
the river Tiber or from wells or springs. The veneration of the 
Romans for springs is a well-known feature of their religious 
tenets. They were preserved with the greatest care, and 
hedged about with careful safeguards against irreverent treat- 
ment or polluting conditions. Apparently after this date the 
people of Rome began to feel the need of a public water-supply 
adequate to meet the requirements of a great city. At any rate, 
in the year 313 B.C. the first aqueduct, called the Appia, for 
bringing public water into the city of Rome was attempted by 
Censors Appius Claudius, Crassus, and C. Plautius, the former 
having constructed the aqueduct, and the latter having found 
the springs. Appius must have been an engineer of no mean 
capacity, for it was he who constructed the first portion of the 
Appian Way. The origin of this water-supply is some springs 
about 10 miles from Rome, and they may now be seen at the 
bottom of stone quarries in the valley of the Anio River. This 



.4A70 VET US. 



39 



aqueduct, Aqua Appia, is mostly an underground waterway, 
only about 300 feet of it being carried on masonry arches. At 
the point where it enters the city it was over 50 feet below the 
surface; its clear cross-section is given as 2-k feet wide by 5 feet 




Claudia, of dimension stone, and Anio Novus, of brick and concrete, on top of it. 

high. The elevation of its water-surface in Rome was probably 
under 60 feet above sea-level. 

27. Anio Vetus. — The next aqueduct built for the water- 
supply of Rome was called Anio Vetus. It was built 272-269 
B.C., and is about 43 miles long; it took its water from the 
river Anio. About 11 00 feet of its length was carried above 
ground on an artificial structure. It also was a low-level aque- 
duct, the elevation at which it delivered water at Rome being 
about 150 feet above sea-level. It was built of heavy blocks of 
masonry, laid in cement, and the cross-section of its channel was 
about 3.7 feet wide by 8 feet high. In the year 144 B.C. the 
Roman senate made an appropriation equal to about $400,000 
of our money to repair the two aqueducts already constructed, 
and to construct a new one called Aqua Marcia, to deliver water 
to the city at an elevation of about 195 feet above sea-level. 
This aqueduct was finished 140 B.C.; it is nearly 58 miles 
long, and carried water of most excellent quality through a 
channel which, at the head of the aqueduct, was 5I feet wide 



40 ANCIENT CIVIL-ENGINEERING WORKS. 

by 8 1\ feet high, but farther down the structure was reduced to 
3 feet wide by 5 1\ feet high. The excellent water of these springs 
is used for the present supply of Rome, and is brought in the 
Aqua Pia, built in 1869, as a reconstruction of the old Aqua 
Marcia. This aqueduct, like its two predecessors, is built of 
dimension stone, 18 inches by 18 inches by 42 inches, or larger, 
laid in cement; but concrete and brick were used in the later 
aqueducts, with the exception of Claudia. 

28. Tepula. — The aqueduct called Aqua Tepula, about 11 
miles in length, and completed 125 B.C., was constructed to 
bring into the city of Rome a slightly warm water from the vol- 
canic springs situated on the hill called Monte Albani (Alban 
Hills) southeast of Rome. The temperature of these springs 
is about 63° Fahr. In the year B.C. 33 Agrippa caused the water 
from some springs high up the same valley to be brought in 
over the aqueduct Aqua Julia, 14 miles long. This latter water 
was considerably colder than that of the Tepula Springs. The 
two waters were united before reaching Rome and allowed to 
flow together far enough to be thoroughly mixed. They were 
then divided and carried into Rome in two conduits. The vol- 
ume of water carried in the Aqua Julia was about three times 
that taken from the Tepula Springs, the cross-section of the 
latter being only 2.7 feet wide by 3.3 feet high, while that of Julia 
was 2.3 feet by 4.6 feet. The water from Aqua Julia entered 
Rome at an elevation of about 212 feet above sea-level, and that 
from Aqua Tepula about 1 1 feet lower. 

29. Virgo. — The sixth aqueduct in chronological order was 
called Virgo, and it was completed 19 B.C. It takes water from 
springs about 8 miles from Rome and only about 80 feet above 
sea-level, but the length of the aqueduct is about 13 miles. 
The delivery of water in the city by this aqueduct is about 67 
feet above that level. The cross-section of this channel is about 
1.6 feet wide and 6.6 feet high. 

30. Alsietina. — The preceding aqueducts are all located on 
the left or easterly bank of the Tiber, but one early structure 
was located on the right bank of the Tiber to supply what was 
called the Trans-Tiberine section of the city, and it was known 
as Aqua Alsietina. The emperor Augustus had this aqueduct 



CLAUDIA. 



41 



constructed during his reign, and it was finished in the year 
A.D. lo. Its source is a small lake of the same name with itself , 
about 20 miles from Rome. The elevation of this lake is 
about 680 feet above sea-level, while the water was delivered at 
an elevation of about 55 feet above the same level. The water 
carried by this aqueduct was of such a poor quality that Fronti- 
nus could not ' ' conceive why such a wise prince as Augustus 
should have brought to Rome such a discreditable and unwhole- 
some water as the Alsietina, unless it was for the use of Nau- 
machia." The latter was a small artificial lake or pond in which 
sham naval fights were conducted. 

31. Claudia. — The eighth aqueduct described by Frontinus 
is the Aqua Claudia, built of dimension stone, which he calls a 




Sand and Pebble Catch-tanks near Tivoli. Dimension-stone aqueducts of Marcia at 
either end of the tank built of small stone; opus incretum. The arches are chambers 
of the tanks. 



magnificent work on account of the large volume of water which 
it supplied, its good quality, and the impressive character of 
considerable portions of the aqueduct itself, between 9 and 
10 miles being carried on arches. It was built in 38-52 a.d. 
and is forty-three miles long. The sources of its supply are 
found in the valley of the Anio, and consequently it belongs 
to the system on the left bank of the Tiber. The cross-section 



42 ANCIENT CIVIL-ENGINEERING WORKS. 

of its channel was about t,.^ feet wide by 6.6 feet high. It was 
a work greatly admired by the Roman people, as is evidenced 
by the praise ' ' given to it by Roman authors who wrote at that 
time." It delivered water at the Palatine 185 feet above sea- 
level. According to Pliny, the combined cost of it and the Aqua 
AnioNovuswas 55,500,000 sestertii, or nearly $3,000,000. This 
aqueduct probably belongs to the highest type of Roman hy- 
draulic engineering. It follows closely the location of the Aqua 
Marcia, although its alignment now includes a cut-off tunnel 
about 3 miles long, the latter having been constructed about 
thirty-six years after the aqueduct was opened. Mr. Clemens 
Herschel observes that the total sum expended for these two 
aqueducts makes a cost of about $6 per lineal foot for the two. 
The arches of this aqueduct and those of the Anio Novus have 
clear spans of 18 to 20 feet, with a thickness at the crown of 
about 3 feet. 

32. Anio Novus. — The ninth aqueduct described by Frontinus 
is called Anio Novus. It was also constructed in the years a.d. 
38-52. This aqueduct has a length of about 54 miles and takes 
its supply from artificial reservoirs constructed by Nero at his 
country-seat in the valley of the Anio near modern Subiaco. 
This structure is built of brick masonry lined with concrete. That 
portion of the Aqua Claudia which is located on the Campagna 
carries for 7 miles the Anio Novus, and it forms the long line 
of aqueduct ruins near Roma Vecchia. The upper surface of 
the arch ring at the crown forms the bottom of the channel of 
the aqueduct. The cross-section of the channel of the Anio 
Novus was 3.3 feet wide by 9 feet high. The elevation of the 
water in this, as in the Claudia, when it reached the Palatine 
was about 185 feet above sea-level. The Anio Novus in some 
respects would seem to be a scarcely less notable work than the 
Claudia. About 8 miles of its length is carried on arches, some 
of them reaching a height of about 105 feet from the ground. 

33. Lengths and Dates of Aqueducts. — These nine aqueducts 
constituted all those described by Frontinus, as no others were 
completed prior to his time. Five others were, however, sub- 
sequently completed between the years 109 a.d. and 306 a.d., 
but enough has already been shown in connection with the older 



INTAKES AND SETTLING-BASINS. 



4:B 



structures to show the character of the water-supply of ancient 
Rome. 

The following tabular statement is a part of that given by- 
Mr. F. W. Blackford in ' ' The Journal of the Association of 
Engineering Societies," December, 1896. It shows the dates 
and lengths of the ancient aqueducts of Rome between the years 
312 B.C. and 226 A.D., with the length of the arch portions. The 
list includes those built up to the end of the Empire. It will be 
observed that the total length of the aqueducts is 346 miles, and 
that of the arch portions 44 miles. The figures vary a little from 
those given by Lanciani and others, but they are essentially 
accurate. 



Name. 



Date. 

B.C. 



Appia 

Anio Vetus . 
Marcia .... 
Tepula. . . . 

Julia 

Virso , 



Alsietina. . . . 
Augusta . . . , 

Claudia 

Anio Novus. . 

Triana 

Alexandrina. 



272-264 

145 
126 

34 
21 

A D. 
10 
10 

SO 

52 
109 
226 



Totals. 



Total 

Length in 

Miles. 



II 

43 

ei 
13 
15 
14 



6 
46 
58 
42 
15 



346 



Length of 

Arches in 

Miles. 



Little 

12 

Little 

6 
Little 

Little 



9 
Little 



44 



34. Intakes and Settling-basins. — The preceding brief de- 
scriptions of the old Roman aqueducts give but a superficial 
idea of the real features of those great works and of the system 
of water-supply of which they were such essential portions. 
Enough has been shown, however, to demonstrate conclusively 
that the engineers and constructors of old Rome were men who, 
on the one hand, possessed a high order of engineering talent 
and, on the other, ability to put in place great structures whose 
proportions and physical characteristics have commanded the 
admiration of engineers and others from the time of their com- 
pletion to the present day. If a detailed statement were to be 



44 ANCIENT CIVIL-ENGINEERING WORKS. 

made in regard to the water-supply of ancient Rome, it would 
appear that much care was taken to insure wholesome and 
potable water. At the intakes of a number of the aqueducts, 
reservoirs or basins were constructed in which the waters were 
first received and which acted as settling-basins, so that as much 
sedimentation as possible might take place. Similar basins 
(picinae) were also constructed at different points along the aque- 
ducts for the same purpose and for such other purposes as the 
preservation of the water in a portion of the aqueduct in case 
another portion had to be repaired or met with an accident 
which for the time being might put it out of use. These basins 
were usually constructed of a number of apartments, the water 
flowing from one to the other, very much as sewage in some 
sewage-disposal works flows at the present time through a series 
of settling-basins. The object of these picinae was the clear- 
ing of the water by sedimentation. Indeed there was in some 
cases a use of salt in the water to aid in clarifying it. This 
is an early type of the modern process of clarifying water by 
chemical precipitation, not the best of potable-water practice, 
but one that is sometimes permissible. 

35. Delivery- tanks. — The aqueducts brought the water to cas- 
tellas or delivery -tanks, i.e., small reservoirs, both inside the 
city and outside of it, and from these users were obliged by law 
to take their supplies ; that is, for baths, for fountains, for public 
uses, for irrigation, and for private uses. When Frontinus wrote 
his ' ' De Aquis ' ' a little less than three tenths of all the water 
brought to Rome by the aqueducts was used outside of the city. 
The remainder was distributed in the city from 247 delivery- 
tanks or small reservoirs, about one sixth of it being consumed 
by 39 ornamental fountains and 591 water-basins. 

36. Leakage and Lining of Aqueducts. — These aqueducts were 
by no means water-tight. Indeed they were subject to serious 
leakage, and Frontinus shows that forces of laborers were 
constantly employed in maintaining and repairing them. As 
has been stated, the older aqueducts were built of dimension 
stones, while the later were constructed of concrete or bricks 
and concrete. The channels of these aqueducts, as well as reser- 
voirs and other similar structures, were made as nearly water- 



GRADE OF AQUEDUCT CHANNELS. 



45 



tight as possible by lining them with a concrete in which pottery, 
broken into fine fragments, was mixed with mortar. 




Claudia and Anio Novus near Porta Furba. Repairs in brickwork and in a composite 
of concrete and brickwork. 



37. Grade of Aqueduct Channels. — The fall of the water-sur- 
face in these aqueducts cannot be exactly determined. The 



46 ANCIENT CIVIL-ENGINEERING WORKS. 

levelling-instruments used by the Romans were simple and, as 
we should regard them, crude, although they served fairly well 
the purposes to which they were applied. They were not suffi- 
ciently accurate to determine closely the slope or grade of the 
water-surface in the aqueduct channels. The deposition of the 
lime from the water along the water- surface on the sides of the 
channels in many cases would enable that slope to be deter- 
mined at the present time, but sufficiently careful examinations 
have not yet been made for that purpose. Lanciani states that 
the slopes in the Aqua Anio Vetus vary from about one in one 
thousand to four in one thousand. An examination of the in- 
crustation on the sides of the Aqua Marcia near its intake makes 
it appear that the slope of the surface was about .06 foot per 100 
feet, which would produce a velocity, according to the formula 
of Darcy, of about 3.3 feet per second. In some aqueducts built 
in Roman provinces it would appear that slopes have been found 
ranging from one in six hundred to one in three thousand. 

38. Qualities of Roman Waters. — The chief characteristic in 
most of the old Roman waters was their extreme hardness. They 
range from 11° to 48° of hardness, the latter belonging to the 
water of the Anio, while the potable waters in this country 
scarcely reach 5°. The old Romans recognized these character- 
istics of their waters and, as has been intimated, used the best 
of them for table purposes, while the less wholesome were em- 
ployed for fountains, flushing sewers, and other purposes not 
affected by undesirable qualities. The water from Claudia, for 
instance, was used for the imperial table. The water from the 
Aqua Marcia was also of excellent quality, while that brought 
in by the Aqua Alsietina was probably not used for potable pur- 
poses at all. 

39. Combined Aqueducts. — In several cases a number of 
aqueduct channels were carried in one aqueduct. A marked 
instance of this kind was that of Julia, Tepula, and Marcia, all 
being carried in vertical series in one structure. Numerous 
instances of this sort occurred. 

40. Property Rights in Roman Waters. — In reading the two 
books of Frontinus one will be impressed by the property values 
which the old Romans created in water rights. The laws of 



AJUTAGES AND UNIT OF MEASUREMENT. 47 

Rome were exceedingly explicit as to the rights of water-users 
and as to the manner in which water should be taken from the 
aqueducts and from the pipes leading from the reservoirs in and 
about the city. The proper methods for taking the water and 
using it were carefully set forth, and penalties were prescribed 
for violations of the laws pertaining to the use of water. There 
were many abuses in old Rome in the administration of the public 
water-supply, and one of the most troublesome duties which 
Frontinus had to perform lay in reforming those abuses and pre- 
venting the stealing of water. The unit of use of water (a 
"quinaria, " whose value is not now determinable) was the vol- 
ume which would flow from an orifice .907 inch in diameter and 
having an area of about .63 of a square inch. Mr. Herschel 
shows that in consequence of the failure of the Romans to under- 
stand the laws of the discharge of water under varying heads, 
the quinaria may have ranged from .0143 cubic foot to .0044 
cubic foot per second or between even wider limits. 

41. Ajutages and Unit of Measurement. — Frontinus describes 
twenty-five ajutages of different diameter, officially approved 
in connection with the Roman system of public water-supply; 
but only fifteen of these were actually used in his day. All of 
these were circular in form, although two others had been used 
prior to that time. They varied in diameter from .907 to 8.964 
English inches and were originally made of lead, but that soft 
metal lent itself too easily to the efforts of unscrupulous water- 
users to enlarge them by thinning the metal. In his time they 
were made of bronze, which was a hard metal and could not be 
tampered with so as to enlarge its cross-section. The discharge 
through the smallest of these ajutages was the quinaria, the unit 
in the scale of water rights. The largest of the above ajutages had 
a capacity of a little over 97 quinarise. 

This unit (the quinaria) was based wholly on superficial area, 
and had no relation whatever to the head over the orifice or to the 
velocity corresponding to that head. Although Frontinus refers 
in several cases to the fact that the deeper the ajutage is placed 
below the water- surface the greater will be the discharge through 
it, also to the fact that a channel or pipe of a given area of cross- 
section will pass more water when the latter flows through it 



48 ANCIENT CIVIL-ENGINEERING WORKS. 

witli a high velocity, he and other Roman engineers seem to have 
failed completely to connect the idea of volume of discharge to 
the product of area of section by velocity. In the Roman mind 
of his day, and for perhaps several hundred years after that, the 
area of the cross-section of the prism of water in motion was the 
only measure of the volume of discharge. This seems actually 
preposterous at the present time, and yet, as observed by Mr. 
Herschel, possibly a majority of people now living have no clearer 
idea of the volume of water flowing in either a closed or open 
channel. Existing statutes even respecting water rights bear 
out this statement, improbable as it may at first sight appear. 
This early Roman view of the discharge is, however, in some 
respects inexplicable, for Hero of Alexandria wrote, probably in 
the period 100-50 B.C., that the section of flow only was not suffi- 
cient to determine the quantity of water furnished by a spring. 
He proceeded to set forth that it was also necessary to know the 
velocity of the current, and further explained that by forming 
a reservoir into which a stream would discharge for an hour the 
flow or discharge of that stream for the same length of time would 
be equal to the volume of water received by the reservoir. His 
ideas as to the discharge of a stream of water were apparently 
as clear as those of a hydraulic engineer of the present time. 
Indeed the method which he outlines is one which is now used 
wherever practicable. 

It has been a question with some whether Frontinus and 
other Roman engineers were acquainted with the fact that a 
flaring or outward ajutage would increase the flow or discharge 
through the orifice. The evidence seems insufficient to establish 
completely that degree of knowledge on their part. At the same 
time, in the CXII. chapter of Frontinus' book on the "Water- 
supply of the City of Rome," he states that in some cases pipes 
of greater diameter than that of the orifice were improperly 
attached to legal ajutages. He then states : " As a consequence 
the water, not being held together for the lawful distance, and 
being on the contrary forced through the short restricted dis- 
tance, easily filled the adjoining larger pipe." He was convinced 
that the use of a pipe with increased diameter under such cir- 
cumstances would give the user of the water a larger supply than 



THE STEALING OF WATER. 49 

that to which he was entitled, and he was certainly right in at 
least most cases. 

The actual unit orifice through which the unit volume of 
water called the quinaria was discharged was usually of bronze 
stamped by a proper official, thus making its use legal for a given 
amount of water. The Roman engineers understood that such 
an orifice should be inserted accurately at right angles to the 
side of the vessel or orifice, and that was the only legal way to 
make the insertion. Furthermore, the law required that there 
should be no change in the diameter of the pipe within 50 feet 
of the orifice. It was well known that a flaring pipe of increased 
diameter apphed immediately at the orifice would largely increase 
the discharge, and unscrupulous people resorted to that means 
for increasing the amount of water to be obtained for a given 
price. 

42. The Stealing of Water. — It appears also that Frontinus 
experienced much trouble from clandestine abstraction of water 
from reservoirs and water-pipes. The administration of the 
water commissioner's office had been exceedingly corrupt prior 
to his induction into office, and some of his most troublesome 
official work arose from his efforts to detect water-thieves, and 
to guard the supply system from being tapped irregularly or 
illegally. We occasionally hear of similar instances of water- 
stealing at the present time, which shows that human nature 
has not altogether changed since the time of Frontinus. 

43. Aqueduct Alignment and Design of Siphons. — ^The align- 
ment of some of the Roman aqueducts followed closely the con- 
tours of the hills around the heads of valleys, while others took 
a more direct line across the valleys on suitable structures, fre- 
quently series of arches. Judging from our own point of view 
it may not be clear at first sight why such extensive masonry 
constructions were used when the aqueduct could have been kept 
in excavation by following more closely the topography of the 
country. There is little doubt that the Romans knew perfectly 
well what they were about. Indeed it is definitely stated in 
some of the old Roman writings that the structures were built 
across valleys for the specific purpose of saving distance which, 
in most instances at least, meant saving in cost. 



50 



ANCIENT CIVIL-ENGINEERING WORKS. 



These masonry structures, it must be remembered, were built 
of material immediately at hand. Furthermore, these aqueducts 
were generally only made of sufficient width for the purpose of 
carrying water-channels. They were not wide structures. In 
some cases they were not more than 8 feet or 9 feet wide for a 
height of nearly 100 feet. The cost of construction was thus 
largely reduced below that of wide structures. 




Old Roman Lead and Terra-cotta Pipe. 

The Romans were perfectly familiar with the construction 
of inverted siphons. As a matter of fact Vitruvius, in Chapter 
VII of his Eighth book, decribes in detail how they should be 
designed, His specific descriptions relate to lead pipes, but it is 
clear from what he states at other points that he considered 
earthenware pipes equally available. He sets forth how the 
pipes should be carried down one slope, along the bottom of the 
valley, and up the other slope, the lowest portion being called 
the ' ' venter." He realized the necessity of guarding all elbows 
m the pipe by using a single piece of stone as a detail for the 



AQUEDUCT ALIGNMENT AND DESIGN OF SIPHONS. 51 

elbow, a hole being cut in it in each direction in which the adjoin- 
ing sections of pipe should be inserted, the sections of lead pipe 
being lo feet long, and even goes so far as to describe the stand- 
pipes that should be inserted for the purpose of allowing air to 
escape. Vitruvius also advises that the water should not only 
be admitted to inverted siphons in a gradual manner, but that 
ashes should be thrown into the water when the siphon is 
first used in order that they may settle into the joints or open 
places so as to close any existing leaks. Lead-pipe siphons, 12 
to 18 inches in diameter, with i inch thickness of metal under 
200 feet head, built in ancient times, have been found at Lyons 
in France. Also a drain-pipe siphon with masonry reinforcement 
was built at Alatri in Italy 125 B.C. to carry water under a head 
of about 340 feet. There are other notable instances of inverted 
siphons constructed and used during the ancient Roman period, 
some of them being of lead pipe imbedded in concrete. 



CHAPTER IV. 

44. Antiquity of Masonry Aqueducts. — Masonry aqueducts, 
either solid or with open arches, were not first constructed by 
the city of Rome ; their origin was much farther back in antiquity 
than that. The Greeks at least used them before the Roman 
engineers, and it is not unlikely that the latter drew their original 
ideas from the former, if indeed they were not instructed by them. 
Nor during the times of the Romans was the construction of 
aqueducts confined to Rome. Wherever Roman colonies were 
created it would appear that vast sums were expended in the 
construction of aqueducts for the purpose of suitably supplying 
cities with water. Such constructions are found at many points 
in Spain, France, and other countries which were in ancient 
times Roman colonies. It is probable that there are not less than 
one hundred, and perhaps many more, of such structures in 
existence at the present time. 

45. Pont du Gard. — Among the more prominent aqueducts 
constructed during the old Roman period and outside of Italy 
were the Pont du Gard at Nismes in the south of France, and 
those at Segovia and Tarragona in Spain. The Pont du Gard 
has three tiers of arches with a single channel at the top. , The 
greatest height above the river Gardon is about 180 feet, and the 
length of the structure along the second tier of arches is 885 
feet. The arches in the lowest tier are 51 feet, 63 feet, and 80.5 
feet in span, while the arches in the highest tier are uniformly 
15 feet 9 inches in span. The thickness of the masonry at the 
top of the structure from face to face is 11 feet 9 inches, and 20 
feet 9 inches at the lower tier of arches, the thickness at the 
intermediate tier being 15 feet. 

The largest arch has a depth of keystone of 5 feet 3 inches, 
while the other arches of the lower tier have a depth of keystone 

52 



AQUEDUCTS AT SEGOVIA, METZ, AND OTHER PLACES. 53 

of 5 feet. The depth of the ring-stones of the small upper arches 
is 2 feet 7 inches. This structure forms a sort of composite 
construction, the lower arches constituting four separate arch- 
rings placed side by side, making a total thickness of 20 feet 9 
inches. The intennediate arches consist of three similar series 
of narrow arches placed side by side, but the masonry of the upper 
tier is continuous throughout from face to face. The three and 
four parallel series of arches of the middle and lowest tiers are 
in no way bonded or connected with each other. There is no 
cementing material in any of the arch-rings, but cement mortar 
was used in rubble masonry or concrete around the channel 
through which the water flowed above the upper tier of small 
arches. This structure is supposed to have been built between 
the years 31 b.c. and 14 a.d. 

46. Aqueducts at Segovia, Metz, and Other Places. — The 
Segovia aqueduct was built by the emperor Trajan about a.d. 
100-115. It is built without mortar, and has 109 arches, but 
30 are modern, being reproductions of the old. It has a length 
of over 2400 feet, and in places its height is about 100 feet. The 
old Tarragona aqueduct is built with two series of arches, 25 
being in the upper series and 11 in the lower. It is 876 feet 
long and has a maximum height of over 80 feet. At Mayence 
there are ruins of an aqueduct about 16,000 feet long. In Dacia, 
Africa, and Greece there are other similar ruins. Near Metz 
are the remains of a large old Roman aqueduct. It consisted 
of a single row of arches, and had no features of particular promi- 
nence. This latter observation, however, could not be made 
of one of the bridges in the aqueduct at Antioch. Although 
the masonry and design of this latter structure were crude, its 
greatest height is 200 feet, and its length 700 feet. The lower 
portion of this structure was a solid wall with the exception of 
two openings, the arches extending in a single row along its upper 
portion. On the island of Mytilene are the ruins of another old 
aqueduct about 500 feet long, with a maximum height of about 
80 feet. 

The building of these remarkable aqueducts was practised 
at least down to the later periods of the Roman empire, that 
of Pyrgos, near Constantinople, — built not earlier than the tenth 



54 ANCIENT CIVIL-ENGINEERING WORKS. 

century, — being an excellent example. It consists of two 
branches at right angles to each other. The greater branch is 
670 feet long, and its greatest height 106 feet. There are three 
tiers of arches, the two upper being of semicircular and the 
lower of Gothic outline. The number in each tier for a given 
height is the same, but with an increasing length of span in rising 
from the lowest to the highest tier. Thus the highest tier of 
piers is the lightest, relieving the top of the structure of weight. 
The lowest row of piers is reinforced by counterforts or buttresses. 
At the top of the structure the width or thickness is 1 1 feet, but 
the thickness increases uniformly to 21 feet at the bottom. The 
smaller branch of the aqueduct is 300 feet long, and was built 
with twelve semicircular arches. 

47. Tunnels. — The construction of tunnels, especially in con- 
nection with the building of aqueducts, constituting a branch 
of engineering procedure, was frequently practised by the ancient 
nations. Large tunnel-works were executed many times by the 
ancient Greeks and Romans. It would seem that the Greeks 
were the instructors of the Romans in this line of engineering 
operations. As early as B.C. 625 we are told that the Greek 
engineer Eupalinus constructed a ttmnel 8 feet broad, 8 feet high, 
and 4200 feet long, through which was built a channel for carry- 
ing water to the city of Athens. 

Sixty-five years later a similar work was constructed for the 
same Grecian city. Indeed it appears that tunnels were con- 
structed in the time of the earliest history of aqueducts built to 
supply ancient Greek and Roman cities with water. 

It is certain that at the beginning of the Christian era tun- 
nelling processes were well known among the Romans. Vitruvius 
writes, in speaking of the construction of aqueducts, in Chap- 
ter VII of the Eighth Book : ' ' If hills intervene between the 
city wall and spring head, tunnels underground must be made, 
preserving the fall above assigned; if the ground cut through 
be sandstone or stone, the channel may be cut therein; but if 
the soil be earth or gravel, side walls must be built, and an arch 
turned over, and through this the water may be conducted. 
The distance between the shafts over the tunnelled part is to be 
120 feet." 



TUNNELS. 



55 



The Romans pierced rock in their tunnel-work, not only by 
chiselling, but sometimes by building fire against the rock so as 
to heat it as hot as possible. The heated rock was then drenched 
with cold water, so that it might be cracked and disintegrated 
to as great an extent as practicable. According to Pliny vinegar 
was used instead of water in some cases, under the impression 
that it was more efficacious. 

One of the methods mentioned by Vitruvius is plainly ' ' the 
cut and cover " procedure of the present day. In Duruy's 




Roman water-pipe made of bored-out blocks of storiC. 

history of Rome a tunnel over three miles long is mentioned on 
a line of an aqueduct at Antibes in France, as well as another 
constructed to drain Lake Fucinus in Italy, about a.d. 50. It is 
there stated that the latter required eleven years' labor of 30,000 
men to build a rock tunnel with a section of 86 to 96 square feet 
18,000 feet long. 

Lanciani, in his "Ancient Rome," states that about a.d. 152 
a Roman engineer (Nonius Datus) began the construction of 
a tunnel in Algeria, and after having carefull}^ laid out the axis 
of the tunnel across the ridge * ' by surveying, and taking the 



56 ANCIENT CIVIL-ENGINEERING WORKS. 

levels of the mountains," left the progress of the work in the 
hands of the contractor and his workmen. After the rather long 
absence from such a work of four years he was called back by the 
Roman governor to ascertain why the two opposite sections of 
the tunnel, as constructed, would not meet, and to take the 
requisite measures for the completion of the work through which 
water was to be conducted to Saldse in a suitable channel. He 
explains that there should have been no difficulty, and that the 
failure of the two headings to meet was due to the negligence of 
the contractor and his assistant, whom he states " had com- 
mitted blunder upon blunder," although he writes, "As always 
happens in these cases, the fault was attributed to the engineer." 
He solved the problem by connecting the two approximately 
parallel tunnels by a transverse tunnel, so that water was finally 
brought to the city of Saldas. 

The art of tunnel construction has been one of the most 
widely practised branches of Civil Engineering from the times 
of the ancient Assyrians, Egyptians, Greeks, Romans, and other 
ancient nations down to the present. 

48. Ostia, the Harbor of Rome. — The capacity of the ancient 
Romans to build harbor-works is shown by what they did at 
Ostia, which was then at the mouth of the Tiber, but is now not 
less than four miles inland from the present shore-line. At the 
Ostia mouth of the river the present annual average advance 
seaward is not less than 30 feet, and at the Fiumicino mouth 
about one third of that amount. 

The ancient port of Ostia is supposed to have been founded 
during the reign of the fourth king Ancus Marcius, but it attained 
its period of greatest importance during the reign of Claudius 
and Trajanus. At that time the fertile portions of the Campania 
had been so largely taken up by the country -places of the wealthy 
Romans that it was no longer possible for the peasantry to culti-. 
vate sufficient ground to yield the grain required by the home 
market of the Romans. Large fleets were consequently engaged 
in the foreign grain- trade of Rome. The wheat and other grain 
required in great quantities was grown mostly in Egypt, although 
Carthage and other countries supplied large amounts. The 
great fleets occupied in this trade made ancient Ostia their 



OSTIA, THE HARBOR OF ROME. 



67 



Roman port. At the present time it has no inhabitants, but 
is a group of complete ruins, with its streets of tombs, baths, 




'^, '-^"m,* ^ ^ '^'^y-''^ -ii^ l^iihSctltrJ'!. 



M a. r s Ti. c ■» ' 



Fig. 13.— Plan of Ostia and Porto. 



palaces, and temples, deeply covered with the accumulations 
of many centuries. Enough excavations have been made along 
the shores of the Tiber at this point to show that the river was 
bordered with continuous and substantial masonry quays, flanked 



58 ANCIENT CIVIL-ENGINEERING WORKS. 

on the land side by successions of great warehouses, obviously 
designed to receive grain, wine, oil, and other products of the 
time. The entrance to this harbor was difficult, as the mouth of 
the river was shallow, with bars apparently obstructing its 
approach. There were no jetties, or other seaward works for 
the protection of vessels desiring to make the harbor. It is 
stated that during one storm nearly or quite two hundred vessels 
were destroyed while they were actually in the harbor. 

49. Harbors of Claudius and Trajan. — The difficulty in enter- 
ing the mouth of the Tiber prompted the emperor Claudius to 
construct another harbor to accommodate the vast commerce 
then centring at the port of Rome. Instead of increasing the 
capacity of Ostia and opening the mouth of the river by deepen- 
ing it, he constructed a new harbor on what was then the sea- 
shore, a short distance from Ostia, and connected it with the 
Tiber by a canal, the extension of which by the natural forces 
of the river has become the Fiumicino, the only present navigable 
entrance to the river. This harbor was enclosed by two walls 
stretching out from the shore, and converging on the sea side to 
a suitable opening left for the entrance of ships. The superficial 
area of this harbor was about 175 acres, but it became insufficient 
during the time of Trajan. He then proceeded to excavate 
inland a hexagonal harbor with a superficial area of about 100 
acres, which was connected both with the harbor of Claudius and 
the canal connecting the latter with the Tiber. These harbor- 
works were elaborate in their fittings for the accommodation 
of ships, and were built most substantially of masonry. They 
showed that at least in some branches of harbor-work the old 
Romans were as good engineers as in the construction of aque- 
ducts, bridges, and other internal public works. The harbors 
at ancient Ostia, including those of Claudius and Trajan, were 
not the only works of their class constructed by the Romans, 
but they are sufficient to show as great advancement in harbor 
and dock work as in other lines of engineering. 

These harbors were practically defenceless and exposed to 
the incursions of pirates, which came to be frequently and suc- 
cessfully made in the days of the declining power of Rome. It 
was therefore rather early in the Christian era that these attacks 



HARBORS OF CLAUDIUS AND TRAJAN. 59- 

discouraged, and ultimately drove away, first, the maritime 
business of the Romans and, subsequently, all the inhabitants 
of these ports, leaving the pillaged remnants of the A^ast harbor- 
works, warehouses, palaces, temples, and other buildings in the 
ruined condition in which they are now found. 



CHAPTER V. 

50. Ancient Engineering Science. — The state of what may 
be called the philosophy or science of engineering construction 
in ancient Rome is admirably illustrated by the work on Archi- 
tecture by Marcus Vitruvius PoUio, who is ordinarily known as 
Vitruvius, and who wrote probably a little more than two thou- 
sand years ago. He calls himself an architect, and his work is 
a classic in that profession of which he claims to be a member. 
Although much of his work was purely architectural, a great 
portion of it, on the other hand, was not architecture as we now 
know it, but civil engineering in the best sense of the term. It 
must be remembered, therefore, that what is here written applies 
to that large portion of his work which is purely civil engineering. 

It will be seen that although he understood really little or 
nothing about the science of civil engineering as we now com- 
prehend it, he perceived many of the general and fundamental 
principles of the best practice of that profession and frequently 
applied them in a manner which would do credit to a modern 
civil engineer. He not only laid down axioms to govern the 
design of civil- engineering structures and machinery for the 
transmission of power, but he also set forth many considerations 
bearing upon public and private health and the practice of sani- 
tary engineering in a way that was highly creditable to the state 
of scientific knowledge in his day. /Speaking of the general 
qualifications of an architect, remembering that that word as 
he understood it includes the civil engineer, he states : ' ' An archi- 
tect should be ingenious, and apt in the acquisition of knowledge ; 
... he should be a good writer, a skilful draughtsman, versed in 
geometry and optics, expert at figures, acquainted with history, 
informed on the principles of natural and moral philosophy, 
somewhat of a musician, not ignorant of the sciences both of 

60 



T7i^TT^*S OF THE PHYSICAL PROPERTIES OF MATERIALS. 61 

law and physics, nor of the motions, laws, and relations to each 
other of the heavenly bodies." Again he adds: ' ' Moral philoso- 
phy will teach the architect to be above meanness in his dealings 
and to avoid arrogance; it will make him just, compliant, and 
faithful to his employer; and, what is of the highest importance, 
it w411 prevent avarice gaining an ascendency over him; for he 
should not be occupied with the thoughts of filling his coffers, 
nor with the desire of grasping everything in the shape of gain, 
but by the gravity of his manners and a good character should 
be careful to preserve his dignity." /' 

These quaint statements of the desirable qualities of a pro- 
fessional man are worthy to be considered rules of good profes- 
sional living at this time fully as much as they were in the days 
of old Rome. His esteem for his profession was evidently high, 
but not higher than the value which every civil engineer should 
put upon his professional-life. The need of a general education 
for a civil engineer is greater now even than in his day, although 
musical accomplishments need not be considered as essential 
in modern engineering practice. That qualification, it is inter- 
esting to observe in passing, was inserted by Vitruvius in order 
to illustrate the wide range of engineering practice in those days 
when the architect-engineer was called upon, among other things, 
to construct catapults and other engines of war, in which a nice 
adjustment of gut ropes was determined by the musical tones 
emitted under the desired tension. 

51. Ancient Views of the Physical Properties of Materials. — 
When it is remembered that the chemical constitution of mate- 
rials used in engineering was absolutely unknown, that no quanti- 
tative determination of physical qualities had been made, and 
that the first correct conception of engineering science had yet 
to be acquired, it is a matter of wonder that there had been 
attained the engineering development evidenced both by ancient 
writings like those of Vitruvius and great engineering works 
like those of Rome, in the Babylonian Plain and in Egypt. In 
discussing the problem of water-supply, he mentions that certain 
learned ancients, "physiologists and philosophers, maintained 
that there are four elements— air, fire, water, and earth — and 
that their mixture, according to the difference of the species, 



62 ANCIENT CIVIL-ENGINEERING WORKS. 

formed a natural mode of different qualities. We must recollect 
that not only from these elements are all things generated, but 
that they can neither be nourished nor grow without their assist- 
ance. ' ' This view of the construction of material things was 
not conducive to a clear comprehension of those physical laws 
which lie at the foundation of engineering science, and it is abso- 
lutely essential that these elementary considerations be kept 
constantly in view in considering the engineering attainments 
of the Romans and other ancient peoples. 

52. Roman Civil Engineers Searching for Water. — In ancient 
times, as at present, it was very important in many cases to 
know where to look for water, and how to make what might 
promise to be a successful search for it. Vitruvius states that 
the sources of water for a supply may easily be found ' ' if the 
springs are open and flowing above ground." If the sources are 
not so evident, but are more obscure, he recommends that ' ' before 
sunrise one must lie down prostrate in the spot where he seeks to 
find it, and, with his chin placed on the ground and fixed, look 
around the place ; for, the chin being fixed, the eye cannot range 
upwards further than it ought and is confined to the level of the 
place. Then where the vapors are seen curling together and 
rising into the air, there dig, because those appearances are not 
discovered in dry places." This method of discovering water- 
supply would be considered by modern engineers at least some- 
what awkward as well as damp and disagreeable in the early 
morning hours. It is not more fantastic, however, or less philo- 
sophical than the use of the divining-rod, which has been prac- 
tised in modern times as well as ancient, and is used even in some 
country districts at the present time. 

Vitruvius does not forget that the local features, including both 
those of soil and of an artificial character, may affect the qual- 
ity of the water and possibly make it dangerous. He, therefore, 
sets forth general directions by which good potable water may be 
found and that of a dangerous nature avoided. The necessity 
of distinguishing between good and bad water was as present 
to his mind and to the minds of the old Roman engineers as to 
civil engineers of the present day, but the means for making a 
successful discrimination were crude and obviously faulty, and 



LOCATING AND DESIGNING CONDUITS. 63 

very often unsuccessful. He set forth, what is well known, that 
rain-water when collected from an uncontaminated atmosphere 
is most wholesome, but proceeds to give reasons which would not 
now be considered in the highest degree scientific. 

In Chapter V of his Eighth Book there are described some 
"means of judging water" so quaint and amusing that they may 
now well be quoted even though no civil engineer would be bold 
enough to cite them in modern hydraulic practice. He says: 
" If it be of an open and running stream, before we lay it on, the 
shape of the limbs of the inhabitants of the neighborhood should 
be looked to and considered. If they are strongly formed, of 
fresh color, with sound legs and without blear eyes, the supply 
is of good quality." At another point he comes rather closely 
to our modern requirements which look to the exclusion of 
minute and elementary vegetable growths, when he says : ' ' More- 
over, if the water itself, when in the spring, is limpid and trans- 
parent, and the places over which it runs do not generate moss, 
nor reeds, nor other filth be near it, everything about it having 
a clean appearance, it will be manifest by these signs that such 
water is light and exceedingly wholesome." 

53. Locating and Designing Conduits. — In "treating of the 
manner of conducting water in pipes or other conduits, he 
adverts to the necessity of accurate levelling and the instruments 
that were used for that purpose. The three instruments which 
he mentions as being used are called the dioptra, the level (libra 
aquaria) , and the chorobates, the latter consisting of a rod about 
20 feet in length, having two legs at its extremities of equal 
length and at right angles to it. Cross-pieces were fastened 
between the rod and the legs with vertical lines accurately 
marked on them. These vertical lines were placed in a truly 
vertical position by means of plumb-lines so that the top of 
the rod was perfectly level, and the work could thus be made 
level in reference to it. 

In Rome the water was generally conducted either by means 
of open channels, usually built in masonry for the purpose, or 
in lead pipes, or in "earthen tubes." Vitruvius states that the 
open channels should be as solid as possible, and have a fall of 
not less than one half a foot in 100 feet. The open channels 



64 ANCIENT CIVIL-ENGINEERING WORKS. 

were covered with an arch top, so that the sun might be kept 
from striking the water. After bringing the water to the cit};- 
it was divided into three parts. One was for the supply of pools 
and fountains, another for the supply of baths, and a third for 
the supply of private houses. A charge was made for the use 
of water for the pools, fountains, and baths, and in this way 
a yearly revenue was obtained. A further charge was also made 
for the water used in private houses, the revenue from which 
was applied for the maintenance of the aqueduct which supplied 
the water. The treatment to be given to the different soils, 
rocks, and other materials through which the conduit was built 
which brought the supply to Rome is duly set forth by Vitru- 
vius, and he describes the conditions under which tunnels were 
constructed. He also described the methods of classifying the 
lead pipes through which water was conducted from the reser- 
voirs to the various points in the city after stating that they 
must be made in lengths of not less than lo feet. The sheets 
of lead employed in the manufacture of the pipes he describes 
as ranging in width from 5 inches to 100 inches. The diameter 
of the pipe would obviously equal very closely the width of the 
sheet divided by the ratio between the circumference and the 
diameter of the corresponding circle. 

54. Siphons. — He speaks of passing valleys in the construc- 
tion of the conduits by means of what we now call siphons, and 
prescribes a method for relieving it of the accumulated air. In 
speaking of earthen tubes or pipes he says that they are to be 
provided not less than 2 inches thick and ' ' tongued at one end 
so that they may fit into one another," the joints being coated 
with quicklime and oil. He further observes that water con- 
ducted through earthen pipes is more wholesome than that 
through lead, and that water conveyed in lead must be injurious 
because from it white lead is obtained, which is said to be injuri- 
ous to the human system. Indeed the eftects of lead-poisoning 
were recognized in those early days, and its avoidance was at- 
tempted. In the digging of wells he wisely states that "the 
utmost ingenuity and discrimination ' ' must be used in the exami- 
nation of the conditions under which wells were to be dug. He 
also appreciated the advantage of sedimentation, for he advises 



HEALTHFUL SITES FOR CITIES. 65 

that reservoirs be made in compartments so that, as the water 
flows from one to another, sedimentation may take place and the 
water be made more wholesome. 

55. Healthful Sites for Cities. — In the location of cities, as 
well as of private residences, Vitruvius lays down the general 
principle that the greatest care should be taken to select sites 
which are healthy and subject only to clean and sanitary sur- 
roundings. J\larshy places and those subject to fogs, especially 
those "charged with the exhalations of the fenny animals," are 
to be avoided. Apparently this reference to "fenny animals" 
may have beneath it the fundamental idea of bacteria, but that 
is not certain. The main point of all these directions for the 
securing of sanitary conditions of living is that, so far as his. 
technical knowledge permitted him to go, he insists on the same 
class of wholesome conditions that would be prescribed by a 
modern sanitary engineer. ' 

56. Foundations of Structures. — Similarly in Chapter V of 
his First Book, on "Foundations of Walls and Towers," Vitru- 
vius shows a realization of the principal conditions needful and 
requisite for the suitable founding of heavy buildings. After 
a sanitary site for a city is determined and one that can be put 
in communication with other people ' ' by good roads, and river 
or sea navigation for the transportation of merchandise," he 
proceeds to state that ' ' foundations should be carried down 
to solid bottom, if such can be found, and that they should be 
built thereon of such thickness as may be necessary for the 
proper support of that part of the wall standing above the natural 
level of the ground. They should be of the soundest workman- 
ship, and materials of greater thickness than the w^alls above." 
Again, in speaking of the foundations supporting columns, he 
states :•' The intervals between the foundations brought up 
ixnder the columns should be either rammed down hard, or 
arched, so as to prevent the foundation-piers from swerving. 
If solid ground cannot be come to, and the ground be loose or 
marshy, the place must be excavated, cleared, and either alder, 
olive, or oak piles, previously charred, must be driven with a 
machine as close to each other as possible and the intervals 
between the piles filled with ashes. The heaviest foundations 



m ANCIENT CIVIL-ENGINEERING WORKS. 

may be laid on such a base." It is thus seen that pile foundations 
were used by the Romans, and that the piles were driven with a 
machine. It would be difficult to give sounder general rules of 
practice even after more than two thousand years' additional 
experience. 

57. Pozzdolana and Sand. — Of all the materials which were 
useful to the Romans in their various classes of construction, 
including the foundations of roads, "pozzuolana" must have 
been the most useful, and that which contributed more to the 
development of successful construction in Rome than any other 
single agent. Vitruvius speaks of it frequently and gives rules 
not only for the use of it in the production of mortar and con- 
crete, but also lays down at considerable length the treatment 
which should be given to lime in order to produce the best re- 
sults. It was common, according to his statements, to use two 
measures of "pozzuolana" with one of lime in order to obtain 
a suitable cementing material. This mixture was used in vary- 
ing proportions with sand and gravel or broken stone to produce 
concrete. He describes the various grades of sands to be found 
about Rome and the manner of using them. The statement 
is made that sand should be free of earth and that the best of 
it was such as to yield a ' ' grating sound " when ' ' rubbed between 
the fingers." This is certainly a good engineering test of sand. 
He prefers pit-sand to either river- or sea-sand ; indeed through- 
out all his directions regarding this particular class of construc- 
tion his rules might be used at the present time with perfect pro- 
priety. 

58. Lime Mortar. — The old Romans had also discovered the 
advisability of allowing lime to stand for a considerable period 
of time after slaking. This insured the slaking of all those small 
portions which were possibly a little hydraulic and therefore 
slaked very slowly. He prescribes as a good proportion two 
parts of sand to one of lime, and also mentions the proportion 
of three to one. He attempts to explain the setting, as we term 
it, of lime, but his explanation in obscure terms, involving quali- 
ties of the elements of fire and air, is not very satisfactory. 

59. Roman Bricks according to Vitruvius. — As is well known, 
the Romans were good brick-makers, and they were well aware 



ROMAN TIMBER. 67 

that bricks made from ' ' ductile and cohesive " " red or white 
chalky ' ' earth were far preferable to those made of more gravelly 
or sandy clay. The Roman bricks were both sun-dried and kiln- 
burned. 

60. Roman Timber. — Timber was a material much used by 
the Romans, and the greater part of that which they used proba- 
bly was grown in Italy, although considerable quantities were 
imported from other localities. Vitruvius writes in consider- 
able detail concerning the selection of timber while standing, 
as well as in reference to its treatment before being used in 
structures. Like every material used by the old Romans in 
construction, the various kinds and qualities of timber received 
careful study from them, and they were by no means novices 
in the art of producing the best results from those kinds of timber 
with which they were familiar. 

61. The Rules of Vitruvius for Harbors. — In Chapter XII of 
his Fifth Book Vitruvius lays down certain general rules for the 
selection and formation of harbors, and it is known that the 
Romans were familiar with elaborate and effective harbor con- 
struction, as is shown by that at Ostia. He appreciates that a 
natural harbor is one which has ' ' rocks or long promontories 
jutting out, which from the shape of the place form curves or 
angles," and that in such places "nothing more is necessary 
than to construct portices and arsenals around them, or passages 
to the markets." He then proceeds to state that if such a natural 
formation is not to be found, and that if " on one side there is a 
more proper shore than on the other, by means of building or of 
heaps of stones, a projection is run out, and in this the enclosures 
of harbors are formed." He then proceeds to explain how ' ' poz- 
zuolana" and lime, in the proportion of two of the former to one 
of the latter, are used in subaqueous construction. He also pre- 
scribed a mode of building a masonry wall up from the bottom 
of an excavation made within what we should call a coffer-dam, 
formed, among other things, ' ' of oaken piles tied together with 
chain pieces." The Romans knew well how to select harbors 
and how to construct in an effective manner the artificial works 
connected with them, although it appears that the effects of tidal 
and river currents in estuaries were neither well understood in 



68 ANCIENT CIVIL-ENGINEERING WORKS. 

themselves nor in their transporting power of the solid material 
which those currents eroded. 

62. The Thrusts of Arches and Earth ; Retaining- walls and 
Pavements. — Although the Romans possessed little or no knowl- 
edge of analytical mechanics they attained to some good quali- 
tative mechanical conceptions. Among other things they under- 
stood fairly well the general character of the thrust of an arch 
and the tendency of the earth to overthrow a retaining-wall. 
Thev knew that a massive abutment was needed to receive safely ' 
the thrust of an arch, and they counterforted or buttressed re- 
taining- walls in order to hold them firmly in place. They also 
realized the danger of wet earth pressing against a retaining-wall, 
and even made a series of offsets or teeth on the inside of the 
wall on which the earth rested in order to aid in holding the wall 
in place. Vitruvius recommends as a safeguard against the 
pressure of earth wet by winter rains that ' ' the thickness of the 
wall must be proportioned to the weight of earth against it," 
and that counterforts or buttresses be employed " at a distance 
from each other equal to the height of the foundations, and of 
the same width as the foundations," the projections at the bot- 
tom being equal in thickne s to that of the wall, and diminishing 
toward the top. 

He gives in considerable detail instructions for the forming 
of pavements and stucco work, so many examples of which are 
still existing in Rome. These rules are in many respects pre- 
cisely the same as would govern the construction of similar 
work at the present time. There are also described in a general 
way the methods of producing white and red lead, as pigments 
of paints, and a considerable number of other pigments of differ- 
ent colors. 

63. The Professional Spirit of Vitruvius. — It is evident, from 
many passages in the writings of this Roman architect-engineer, 
that the ways of the professional men in old Rome were not 
always such as led to his peace of mind. Vitruvius utters bitter 
complaints which show that he did not consider purely pro- 
fessional knowledge and service to be adequately recognized 
or appreciated by his countrymen. /He writes that in the city 
of Ephesus an ancient law provided that if the cost of a given 



MECHANICAL APPLIANCES OF THE ANCIENTS. GO 

work completed under the plans and specifications of an archi- 
tect did not exceed the estimate, he was commended ' ' with 
decrees and honors," but if the cost exceeded the estimate 
with 25 per cent added thereto, he "was required to pay that 
excess out of his own pocket." Then he exclaims, "Would to 
God that such a law existed among the Roman people, not only 
in respect to their public but also to their private buildings, for 
then the unskilful could not commit their depredations with 
■ impunity, and those who were the most skilful in the intricacies 
of the art would follow the profession ! ' ' 

64. Mechanical Appliances of the Ancients. — It is well known 
that the ancients possessed at least some simple types of machines, 
for the reason that they raised many great stones to a consider- 
able height in completed works after having transported them 
great distances from the quarries whence they were taken. 
Undoubtedly these machines were of a simple and crude char- 
acter and were made effective largely by the power of great 
numbers of men. We are not acquainted with all the details 
of these machines, although the general types are fairly well 
known. The elementary machines, including the lever, the 
inclined plane, the pulley, and the screw, which is only an appli- 
cation of the inclined plane, were all used not only by the Romans, 
but probably by every civilized ancient nation. Vitruvius 
describes a considerable number of these machines, and from his 
descriptions it is clear that they had wide application in the 
structural works of the Romans. The block and fall, as we 
term the pulley at the present time, was a common machine in 
the plant of a Roman constructor, as were also various modifica- 
tions and applications of the lever, the roller, and the inclined 
plane. 

65. Unlimited Forces and Time. — It is neither surprising nor 
very remarkable that with the use of these simple machines, 
aided by a practically unlimited number of men, the necessary 
raising or other movement of heavy weights was accomplished 
by the Romans and other ancient peoples. It is to be borne 
in mind that the element of time was of far less consequence 
in those days than at present, and that the rate of pro- 
gress made in the construction of most if not all ancient en- 
gineering works was what we should consider intolerably slow. 



PART I!. 

BRIDGES 



CHAPTER VI. 

66. Introductory. — Although the bridge structures of to-day 
serve the same general purposes as those served by the most 
ancient structures, they are very different engineering products. 
It is not long, in comparison with the historic and prehistoric 
periods during which bridges have been built, since the science 
of mechanics has been sufficiently developed to make bridge 
design a rational procedure; and it is scarcely more than a cen- 
tury since the principles of mechanics were first applied to the 
design of bridge structures in such a way as to determine even 
approximately the amount of stress produced in any member 
by the imposed load. Naturally the first efforts made toward 
a truly rational bridge design were in fact simple and crude and 
only loosely approximate in their results. Probably the first 
analytic treatment of bridges was given to the design of arches 
in masonry and then in cast iron. As the action of forces in 
structures became better known through the development of 
mechanical science, the applications of the latter became less 
crude and approximate and the approach to the refined accuracy 
of the present day was begun. 

67. First Cast-iron Arch. — These older structures, nearly all 
of them arches or more or less related to the arch, first appeared 
in cast iron in the latter part of the eighteenth century, when noth- 
ing like an accurate analysis of forces developed by the applica- 

70 



EARLY TIMBER BRIDGES IN AMERICA. 71 

tion of a given load was known. The first cast-iron arch was 
erected over the Severn in England near Coalbrookdale in the 
year 1779. This bridge had a span of 100 feet, and the under 
surface of the arch or soffit at the crown was 45 feet above the 
points at the abutment from which the arch sprang, or, as civil 
engineers put it, the arch had a span of 100 feet and a rise or 
versine of 45 feet. Other cast-iron arches were built in England 
soon after. 

68. Early Timber Bridges in America. — Timber bridges have 
been built since the earliest historic periods and even earlier, 
but the widest and boldest applications of timber to bridge struc- 
tures have been made in this country, beginning near the end 
of the eighteenth century and running to the middle of the nine- 
teenth century, when timber began to be displaced by iron. 
Timber bridges and those of combined iron and timber are built 
to some extent even at the present day, but the most extended 
work of this class is to be found in the period just named. 

In 1660 w^hat was called the ' ' Great Bridge " w^as built across 
the Charles River near Boston, and was a structure on piles. 
Other similar structures followed, but the first long-span timber 
bridge, where genuine bridge trussing or framing was used, 
appears to have been completed in 1792, when Colonel William P. 
Riddle constructed the Amoskeag Bridge across the Merrimac 
River at Manchester, N. H., in six spans of a little over 92 feet 
from centre to centre of piers. From that time timber bridges, 
mostly on the combined arch and truss principle, were built, 
many of them examples of remarkably excellent engineering 
structures for their day. Among these the most prominent 
were the Bellows Falls Bridge, in two spans of 184 feet each from 
centre to centre of piers, over the Connecticut River, built in 
1785-92 by Colonel Enoch Hale; the Essex-Merrimac Bridge 
over the Merrimac River, three miles above Newburyport, Mass., 
built by Timothy Palmer in 1792, consisting actually of two 
bridges with Deer Island between them, the principal feature 
of each being a kind of arched truss of 160 feet span on one side 
of the island and 113 feet span on the other; the Piscataqua 
Bridge, seven miles above Portsmouth, N. H., in which a "stu- 
pendous arch of 244 feet cord is allowed to be a masterly piece 



7^ BRIDGES. 

of architecture, planned and built by the ingenious Timothy 
Palmer of Newbur3^port, Mass.," in 1794; the so-called "Per- 
manent Bridge" over the Schuylkih River at Philadelphia, built 
in 1804-06 in two arches of 150 feet and one of 195 feet, all in 
the clear, after the design of Timothy Palmer; the Waterford 
Bridge over the Hudson River, built in 1804 by Theodore Burr, 
in four combined arch and truss spans, one of 154 feet, one of 
161 feet, one of 176 feet, and the fourth of 180 feet, all in the 
clear; the Trenton Bridge, built in 1804-06 over the Delaware 
River at Trenton, N. J., by Theodore Burr, in five arch spans of 
the bowstring type, ranging from 161 feet to 203 feet in the 
clear; a remarkable kind of wooden suspension bridge built by 
Theodore Burr in 1808 across the Mohawk River at Schnectady, 
N. Y., in spans ranging in length from 157 feet to 190 feet; the 
Susquehanna Bridge at Harrisburg, Pa., built by Theodore Burr 
in 1812-16 in twelve spans of about 210 feet each; the so-called 
Colossus Bridge, built in 181 2 by Lewis Wernwag over the Schuyl- 
kill River at Fairmount, Pa., with a clear span of 340 feet 3! 
inches; the New Hope Bridge, built in 18 14 over the Delaware 
River, in six 175 feet combined arch and truss spans, and a 
considerable number of others built by the same engineer. 

Some of these wooden bridges, like those at Easton, Pa., and 
at Waterford, N. Y., remained in use for over ninety years with 
only ordinary repairs and with nearly all of the timber in good 
condition. In such cases the arches and trusses have been 
housed and covered with boards, so as to make what has been 
commonly called a covered bridge. The curious timber sus- 
pension bridge built by Theodore Burr at Schenectady was 
used twenty years as originally built, but its excessive deflection 
under loads made it necessary to build up a pier under the middle 
of each span so as to support the bridge structure at those points. 
These bridges were all constructed to carry highway traffic, but 
timber bridges to carry railroad traffic were subsequently built 
on similar plans, except that Burr's plan of wooden suspension 
bridge at Schenectady was never repeated. 

69. Town Lattice Bridge. — A later type of timber bridge 
which was most extensively used in this country was invented 
by Ithiel Town in January, 1820, which was known as the Town 



EARLY TIMBER BRIDGES IN AMERICA. 



7'6 




'K 



74 



BRIDGES. 



lattice bridge. This timber bridge was among those used for 
raihoad structures. As shown by the plan it was composed of 
a close timber lattice, heavy plank being used as the lattice 
members, and they were all joined by wooden pins at their inter- 





" >''■ ■ ''' ■''■ " '■ I ' ■ ' '■' ' ■ L '■ \ —. J "'' ' ' l ull 




TOm^ LATTICE TRUSS. 



Fig. 3. 

sections. This type of timber structure was comparatively com- 
mon not longer ago than twenty-five years, and probably some 
structures of its kind are still in use. The close latticework with 
its many pinned intersections made a very safe and strong frame- 
work, and it enjoyed deserved popularity. It was the fore- 
runner in timber of the modern all-riveted iron and steel lattice 
truss. It is of sufficient significance to state, in connection with 
the Town lattice, that its inventor claimed that his trusses could 
be made of wrought or cast iron as well as timber. In many 
cases timber arches were combined with them. 

70, Howe Truss. — The next distinct advance made in the 
development of bridge construction in the United States was 
made by brevet Lieutenant-Colonel Long of the Corps of Engi- 
neers, U.S.A., in 1830-39, and by William Howe, who patented 
the bridge known as the Hov/e truss, although the structure 
more lately known under that name is a modification of Howe's 
original truss. Long's truss was entirely of timber, including 
the keys, pins, or treenails required, and it was frequently built 



HOWE TRUSS. 



75 



CO 








76 BRIDGES. 

in combination with the wooden arch. The truss was consider- 
ably used, but it was not sufficiently popular to remain in use. 

The Howe truss was not an all-wooden bridge. The top and 
bottom horizontal members, known as ' ' chords, ' ' the inclined 
braces between them and the vertical end braces, all connecting 
the two chords, were of timber, and they were bolted at all inter- 
sections; but the vertical braces were of round iron with screw 
ends. These rods extended through both chords and received 
nuts at both ends pressing on cast-iron washers through which 
the rods extended. These wrought-iron round rods were in 
groups at each panel-point, numbering as many as existing 
stresses required. The ends of the timber braces abutted against 
cast-iron joint-boxes. The railroad floor was carried on heavy 
timber ties running entirely across the bridge and resting upon 
the lower chord members. It was a structure simple in char- 
acter, easily framed, and of materials readily secured. It was 
also easily erected and could quickly be constructed for any 
reasonable length of span. It possessed so many merits that it 
became widely adopted and is used in modified form at the 
present day, particularly on lines where the first cost of con- 
struction must be kept as low as possible. The large amount 
of timber in it and the simple character of its wrought-iron or 
steel members greatly reduces its first cost. 

71. Pratt Truss. — In 1844 the two Pratts, Thomas W. and 
Caleb, patented the truss, largely of timber, which has since 
been perpetuated in form by probably the largest number of iron 
and steel spans ever constructed on a single type. The original 
Pratt trusses had timber upper and lower chords, but the vertical 
braces were also made of timber instead of iron, while the inclined 
braces were of round wrought iron with screw ends, the reverse 
of the web arrangement in the Howe type. This truss had the 
great advantage of making the longest braces (of iron) resist 
tension only, while the shorter vertical braces resist compression. 
As a partially timber bridge it could not compete with the Howe 
truss, because it contained materially more iron and consequently 
was more costly. This structure practically closed the period 
of development of timber bridges. 



SQUIRE WHIPPLE'S WORK. 77 

72. Squire Whipple's Work. — What amounted to a new epoch 
in the development of bridge construction in this country prac- 
tically began in 1840 when Squire Whipple built his first bow- 
string truss with wrought-iron tension and cast-iron compression 
members. While the Pratts and Howe had begun to employ 
to some extent the analysis of stresses in the design of their 
bridge members, the era of exact bridge analysis began with 
Squire Whipple. He subjected his bridge designs to the exacting 
requirements of a rational analysis, and to him belongs the honor 
of placing the design of bridges upon the firm foundation of a 
systematic mathematical analysis. 

73. Character of Work of Early Builders. — The names of 
Palmer, Burr, and Wernwag were connected with an era of ad- 
mirable engineering works, but, with bridge analysis practically 
unknown, and with the simplest and crudest materials at their 
disposal, their resources were largely constituted of an intuitive 
engineering judgment of high quality and remarkable force in 
the execution of their designs never excelled in American engi- 
neering. They occasionally made failures, it is true, but it is not 
recorded that they ever made the same error twice, and the works 
which they constructed form a series of precedents which have 
made themselves felt in the entire development of American 
bridge building. 



CHAPTER VII. 

74. Modem Bridge Theory.— The evolution of bridge design 
having reached that point where necessity of accurate analysis 
began to make itself felt, it is necessary to recognize some of the 
fundamental theoretical considerations which lie at the base of 
modem bridge theory, and which involve to a considerable extent 
that branch of engineering science known as the elasticity or 
strength of the materials used in engineering construction. 

The entire group of modern bridge structures may be divided 
into simple beams or girders, trusses, arches, suspension bridges, 
and arched ribs, each class being adapted to carry either highway 
or railway traffic. That class of structure known as beams or 
girders is characterized by very few features. There are solid 
beams like those of timber, with square or rectangular cross- 
sections, and the so-called flanged girders which are constituted 
of two horizontal pieces, one at the top and the other at the 
bottom, connected by a vertical plate running the entire length 
of the beam. The fundamental theory is identically the same 
for both and is known as the "common theory of flexure," i.e., 
the theory of beams carrying loads. 

If an ordinary scantling or piece of timber of square or rect- 
angular cross-section, like a plank or a timber joist, so commonly 
used for floors, be supported at each end, it is a matter of com- 
mon observation that it will sustain an amount of load depending 
upon the dimensions of the stick and length of span. When 
such a bar or piece is loaded certain forces or stresses, as they are 
called, are brought into action in its interior. The word ' ' stress ' ' 
is used simply to indicate a force that exists in the interior of 
any piece of material. It is a force and nothing else. It is 
treated and analyzed in every way precisely as a force. If the 
stresses or forces set up by the loading in the interior of the bar 

78 



THE STRESSES IN BEAMS. 



79 



become greater than the material can resist, it begins to break, 
and the breaking of that portion of the timber in which the 
stresses or forces are greatest constitutes its failure. The load 
which produces this failure in a beam is called the breaking load 
of the beam. In engineering practice all beams are so designed 
or proportioned that the greatest load placed on them shall be 
only a safe percentage of the breaking load ; the safe load usually 
being found between ^ and | of the breaking load. In most 
buildings the safe or working load, as it is called, is probably 
about I of the breaking load. 

75. The Stresses in Beams. — The proper design of beams or 
girders to carry prescribed loads is based upon the stresses which 
are developed or brought into action by them. It can easily 
be observed that if a beam supported at each end be com- 
posed of a number of thin planks or boards placed one upon 
the other, it will carry very little load. Each plank or board 
acts independently of the others and a very small load will cause 
a sag, as shown in Fig. 6. If there be taken, on the other hand. 



5S^ 



--:- Fig. 5. 




Fig. 6. 



t-i Fig. 7. 



a beam made of a single stick of timber of the same width and 
depth as the number of planks shown in Fig. 6, so as to secure 
the solid beam shown in Fig. 7, it is a further common observa- 
tion that this latter beam may carry many times the load which 
the laminated beam, shown in Fig. 6, sustains. The thin planks 
or boards readily slide over each other, so that the ends present 



80 



BRIDGES. 



the serrated form shown in Fig. 6. The preventing of this slid- 
ing is the sole cause of the greatly increased stiffness of the solid 
beam shown in Fig. 7, for there is thus developed along the 
imaginary horizontal sections in the solid beam of Fig. 7 what 
are called shearing forces or stresses ; and since they exist on 
horizontal sections or planes running throughout the entire 
length of the beam, they are called horizontal shears. 

At each end of the beam shown in Fig. 7 there will be an 
upward or supporting force exerted by the abutments on which 
the ends of the beam rest. Those upward or supporting forces 
are shown at R and R' and are called reactions, because the 
abutments, so to speak, react against the ends of the beam when 
the latter is loaded. These reactions depend for their value 
on the amount and the location of the loading which the beam 
carries. Obviously these upward forces or reactions tend to 
cut or shear off the ends of the beam immediately above them, 
and if the loads were sufficiently large and the beam kept from 
bending, the reactions would actually shear off those ends, just 
as punches or shears in a machine-shop actually shear off the 
metal when the rivet-hole is punched, or when a plate is cut by 
shearing into two parts. The beam, however, bends or sags 
before shearing apart actually takes place. 

76. Vertical and Horizontal Shearing Stresses. — If it be sup- 
posed that the length of the beam is divided into a great number 



Wl w„ 




Fig. 8. Fig. 9. 

of parts by imaginary vertical lines, like those shown in Fig. 8, 
then vertical shearing forces will be developed in those vertical 
planes and sometimes, though not often, they are enough to 



VERTICAL AND HORIZONTAL SHEARING STRESSES. 81 

cause failure. It is not an uncommon thing, on the other hand, 
in timber to have actual shearing failure take place along a hori- 
zontal plane through the centre of the beam. Indeed this is 
recognized frequently as the principal method of failure in very- 
short spans. When this horizontal shearing failure takes place, 
the upper and lower parts of the beam slide over each other and 
act precisely like the group of planks shown in Fig. 6. 

If, then, the loaded beam be divided by vertical and hori- 
zontal planes into the small rectangular portions shown in Figs. 
8 and 9, on each such vertical and horizontal imaginary plane 
there will be respectively vertical and horizontal shearing forces, 
which are shown by arrows in Fig. 9. It will be noticed in 
that figure that in each comer of the rectangle the two shearing 
forces act either toward or from each other; in no case do the 
two adjacent shearing forces act around the rectangle in the 
same direction. This is a condition of shearing stresses peculiar 
to the bent beam. It can be demonstrated by theory and is 
confirmed by experiment. There is a further peculiarity about 
these shearing forces which act in pairs either toward or from 
the same angle in any rectangle, and it is that the two stresses 
adjacent to each other have precisely the same value per square 
inch (or any square unit that may be used) of the surface on 
which they act. These stresses per square inch vary, however, 
either along the length of the beam or as the centre line of 
any normal cross-section is departed from. They are greatest 
along the centre line or central horizontal plane represented 
by AB, and they are zero at the top and bottom surfaces of the 
beam. 

Inasmuch as the horizontal shear along the plane A'B' is 
less than that along AB in Fig. 9, a part of the latter has been 
taken up by the horizontal fibres of the beam lying between the 
two planes. In other words, the horizontal layer of fibres at 
A'B' is subjected to a greater stress or force along its length than 
at AB. The same general observation can be made in reference 
to any horizontal layer of fibres that is farther away from the 
centre than another. Hence the farther any fibre is from the 
centre the greater will be the stress or force to which it is sub- 
jected in the direction of its length. It results, then, that the 



82 BRIDGES. 

horizontal layers of fibres which are farthest from the centre line 
of the beam, i.e., those at the exterior surfaces, will be subjected 
to the greatest force or stress, and that is precisely what exists 
in a loaded beam whatever the material may be. 

77. Law of Variation of Stresses of Tension and Compression. 
— Since a horizontal beam supported at each end is deflected 
or bent downward when loaded, it will take a curved form like 
that shown in either Fig. 7 or Fig. 10; but this deflection can 
only take place by the shortening of the top of the beam and the 
lengthening of its bottom. This shows that the upper part of 
the beam is compressed throughout its entire length, while the 
lower part is stretched. In engineering language, it is stated 
that the upper part of the beam is thus subjected to compression 
and the lower part to tension. The horizontal layers or fibres 
receive their tension and compression from the vertical and hori- 
zontal shearing forces in the manner already explained. If the 
conditions of loading of the bent beam should be subjected to 
mathematical analysis, it would be found that throughout the 
originally horizontal plane AB, Fig. 7, passing through the centre 
of each section there would be no stress of either tension or com- 
pression, although the horizontal shearing stress there would be 
a maximum. Further, as this central plane is departed from 
the stress of tension or compression per square inch m any vertical 
section would be found to increase directly as the distance from 
it. This is a very simple law, but one of the greatest importance 
in the design of all beams and girders, whatever may be the form 
or size- of cross-section. It is a law, which applies equally to the 
solid timber beam and to the flanged steel girder, whether that 
girder be rolled in the mill or built up of plates and angles or 
other sections in the shop. It is a fundamental law of what is 
called the common theory of flexure, and is the very foundation 
of all beam and girder design. The horizontal plane represented 
by the line AB m. Fig. 8, along which there is neither tension nor 
compression, is called the "neutral plane," and its intersection 
with any normal cross-section of the beam is called the ' ' neutral 
axis" of that section. Mathematical analysis shows that the 
neutral plane passes through the centres of gravity of all the 
normal sections of the beam and, hence, that the neutral axis 



FUNDAMENTAL FORMUL^^ OF THEORY OF BEAMS. 



83 



passes through the centre of gravity of the section to which it 
belongs. 

78. Fundamental Formulae of Theory of Beams. — The funda- 
mental formulee of the theory of loaded beams may 'be quite 
simply written. Fig. 10 exhibits in a much exaggerated manner 
a bent beam supporting any system of loads W^, W^, W^, etc., 




Fig. II. 

while Fig. 11 shows a normal cross-section of the same beam. 
In Fig. 10 AB is the neutral line, and in Fig. 11 CD is the neutral 
axis passing through the centre of gravity, e.g., of the section. 

If a is the amount of force or stress on a square inch (or other 
square unit), i.e., the intensity of stress, at the distance of unity 
from the neutral axis CD of the section, then, by the fundamental 
law already stated, the amount acting on another square inch at 
any other distance z from the neutral axis will be az. This quan- 
tity is called the "intensity of stress" (tension or compression) 
at the distance z from the neutral axis. Evidently it has its 



84 BRIDGES. 

greatest values in the extreme fibres of the section, i.e., ad and 
ad^. At the neutral axis az becomes equal to zero. FG in Fig. 
1 1 represents the same line as FG in Fig. i o. If the line FH in Fig. 
II be laid down equal to ad and at right angles to FG, and if O 
represent the centre of gravity, e.g., of the section, then let the 
straight line LH be drawn. Any line drawn parallel to FH 
from FG to LH will represent the intensity of stress in the 
corresponding part of the beam's cross-section. Obviously, as 
these lines are drawn in opposite directions from FG, those above 
will indicate stress of one kind, and those below that point 
stress of another kind, i.e., if that above be tension, that below 
will be compression. It can be demonstrated by a simple process 
that the total tension on one side of the neutral axis is just equal 
to the total compression on the other side, and from that condition 
it follows that the neutral axis must pass through the centre of 
gravity or centroid of the section. 

Returning to the left-hand portion of Fig. 1 1 , let dA represent 
a very small portion of the cross-section ; then will az . dA be the 
amount of stress acting on it. The moment of this stress or 
force about the neutral axis will be azdA .z = az^.dA. If this 
expression be applied to every small portion of the entire section, 
the aggregate or total sum of the small moments so found will 
be the moment of all the stresses in the section about the neutral 
axis. That moment will have the value 

M = faz\dA=afz'd.A=aI (i) 

In equation (i) the symbol /*means that the sum of all the 

small quantities to the right of it is taken, and / stands for that 
sum which, in the science of mechanics, is called the moment of 
inertia of the cross-section about its neutral axis. The value of 
the quantity / may easily be computed for all forms of section. 
Numerical values belonging to all the usual forms employed in 
engineering practice are found in extended tables in the hand- 
books of the large iron and steel companies of the country, so 
that its use ordinarily involves no computations of its value. 

Equation (i) may readily be changed into two other forms 
for convenient practical use. In Fig. lo mn is supposed to be 



PRACTICAL APPLICATIONS. 85 

a very short portion of the centre Hne of the beam represented 
by dl. Before the beam is bent the section FG is supposed to 
have the position MN parallel to PQ. Also let u be the small 
amount of stretching or compression (shortening) of a unit's 
length of fibre at unit's distance from the centre line AB oi the 
beam, then will udl and uzdl be the short lines parallel to GN 
in the triangle GmN shown in the figure. The point C is the 
centre of curvature of the line mn, and Cn = Cm is the radius. 
The two triangles Cnm and mNG are therefore similar, hence 

udl mn dl 1 , . 

- — = — ^=— ; .-. w = - (2) 

I p p p 

If the quantity called the coefficient or modulus of elasticity be 
represented by E, then, by the fundamental law of the theory 
of elasticity in solid bodies, 

-a=Eu (3) 

As has already been shown, the greatest stresses (intensities) 
in the section are -\-ad (tension) and —ad^ (compression). If 
K represent that greatest intensity of stress, then 

' ' K = ad, and a = - . . . . . . . (4) 

If the value of a from equation (4) be substituted in equation (i), 

^-f (5) 

79. Practical Applications. — Equation (5) is a formula con- 
stantly used in engineering practice. All quantities in the second 
member are known in any given case. K is prescribed in the 
specifications, and is known as the "working resistance" in the 
design of beams and girders. For rolled steel beams in buildings 
it is frequently taken at 16,000 pounds, i.e., 16,000 pounds per 
square inch, about one fourth the breaking strength of the steel. 
In railroad-bridge work it maybe found between 10,000 and 12,000 
pounds, or approximately one fifth of the breaking strength of 
the steel. The quantities / and d depend upon the form and 
dimensions of the cross-section, and are either known or may be 
determined. The quotient 7 -^ (i is now known as the "section 
modulus," and its numerical values for all forms of rolled beams 



86 BRIDGES. 

can be found in published tables. The use of equation (5) is 
therefore in the highest degree convenient and practicable. 

80. Deflection. — It is frequently necessary, both in the design 
of beams and framed bridges, to ascertain how much the given 
loading will cause the beam or truss to sag, or, in - engineering 
language, to deflect below the position occupied when unloaded. 
The deflection is determined by the sagging in the vertical plane 
of the neutral line below its position when the structure carries 
no load. In Fig. 10 the curved line AB is the neutral line of 
the beam when supporting loads. If the loads should be removed, 
the line AB would return to a horizontal position. The line 
drawn horizontally through A and indicated by x is the position 
of the centre line of the beam before being bent. The vertical 
distance w below this horizontal line shows the amount by which 
the point at the end of the line x is dropped in consequence of 
the flexure of the beam. The vertical distance w is therefore 
called the deflection. Evidently the deflection varies with the 
amount of loading and with the distance from the end of the 
beam. The curved line AB in one special case only is a circle. 
The general character of that curve is determined by the loading 
and the length of span. 

In order that the deflection may be properly considered it 
is necessary that the relation between x and w shall be estab- 
lished for all conditions of loading and length of span. If the 
value of u from equation (2) be placed in equation (3), there will 
result 

a=- (6) 

P 

If the value of a from equation (6) be substituted in the last 
member of equation (i), there will at once result 

Fl 
M = ~ (7) 

P 

It is established by a very simple process in differential cal- 
culus that 

I d^w , . 

p ax^ 



BENDING MOMENTS AND SHEARS WITH SINGLE LOAD. 87 
Hence, substituting from equation (8) in equation (7), 

^=^^'^ w 

Equation (9) may be used by means of some very simple 
operations in integral calculus to determine the value of w in 
terms of x and the loads on the beam when the value of the bend- 
ing moment M is known, and the procedures for determining 
that quantity will presently be given. 

Using the processes of the calculus, the two following equa- 
tions will immediately be found : 

'^^^^jMdx- (10) 



iJfMd.^ (") 



w = 
EI 

As already explained, numerical values for both E and / may 
be taken at once from tables already prepared for all materials 
and for all shapes of beams ordinarily employed in structural 
work, so that equation (11) enables the deflection or sag of the 

bent beam to be computed in any case. The expression -^ is 

dx 

the tangent of the angle made by the neutral line of a bent beam 

with a horizontal line at any given point, and it is a quantity 

that it is sometimes necessary to determine, dw and dx are 

indefinitely short vertical and horizontal lines respectively, 

as shown immediately to the left of B in Fig. 10. 

Equation (11) is not used in structural work nearly as much 
as equation (5), but both of them are of practical value and in- 
volve only simple operations in their use. 

81. Bending Moments and Shears with Single Load. — The 
second members of equations (5) and (9) exhibit values of the 
moments of the internal forces or stresses in any normal cross- 
section of a bent beam about the neutral axis of the section, 
while the values of M must be expressed in terms of the external 
forces or loading. Inasmuch as the latter moment develops just 
the internal moment, it is obvious that the two must be equal. 
In order to write the value of the external moment in terms of 



88 BRIDGES. 

any loading, it is probably the simplest procedure to consider 
a beam carrying a single load. In Fig. 12, AB is such a beam, 
and 1^ is a load which may be placed anywhere in the span, 
whose length is /. The distances of the load from the abutments 
are represented by x^ and x^. The reactions or supporting forces 
exerted under the ends of the beam at the abutments are shown 
by R and R'. The reactions, determined by the simple law of 
the lever, are 



R=W' 



and R'=W-^' (12) 



The greatest bending moment in the beam will occur at the point 
of application of the load, and its value will be 

M,=Rx, = W^=-R% (13) 



R-rrfTT 




Mi=Ra-i=— Ra:2 = 



Fig. 12. 

The bending moments at the end of the beam are obviously zero, 
and the second and fourth members of equation (13) show that 
the moment increases directly as the distance from either end. 
Hence in the lower portion of Fig. 12, at D, immediately under 
the load W, the line DC is laid off at any convenient scale to 
represent the moment M^. The straight lines AC and CB are 
then drawn. Any vertical intercept, 'as FH or KL, between 
AB and either AC or CB will represent the bending moment 
at the corresponding point in the beam. The simple triangular 
diagram ACB therefore represents the complete condition of 
bending of the beam under the single load W placed at any point 
in the span. 



BENDING MOMENTS AND SHEARS WITH ANY LOADS. 89 

The beam AB is supposed for the moment to have no weight. 
Consequently the only force acting upon the portion of the beam 
AO is the reaction R, and, similarly, R' is the only force acting 
upon the portion OB. Obviously so far as the simple action of 
these two forces or reactions is concerned, the tendency of each 
is to cause vertical slices of the beam, so to speak, to slide over 
each other. In other words, in engineering language, the por- 
tion ^0 of the beam is subjected to the shear S = R, while OB 
is subjected to the shear S' = —R\ The cross-sectional area of 
the beam must be sufficient to resist the shear S or S\ The 
upper part of Fig. 13 shaded with broken vertical lines indicates 
this condition of shear. It is evident from this simple case that 
the total vertical shears at the ends of any beam will be the 
reactions or supporting forces exerted at those ends, and that 
each will remain constant for the adjoining portion of the beam. 

The third member of equation (13) shows that the greatest 
bending moment M^ in the beam varies as the product x^x^ 
of the segments of the span. That product will have its greatest 
value when Xj^=x^. Hence a simple beam loaded by a single 
weight will be stibjected to the greatest possible bending moment 
when the weight is placed at the middle of the span, at which point 
also that moment will be found. 

82. Bending Moments and Shears with any System of Loads. — 
The general case of a simple beam loaded with any system of 
weights whatever may be represented in Fig. 13, in which the 
beam of Fig. 12 is supposed to carry three loads, w^, w^, w^. The 
spacing of the loads is as shown. The reactions or supporting 
forces R' are determined precisely as in Fig. 12, each reaction in 
this case being the resultant of three loads instead of one. Apply- 
ing the law of the lever as before, the reaction R will have the 
value 

R = W,^+W,i±^ + wf-±^+^. . . . (14) 

A similar value may be written for R' , but it is probably 
simpler, after having found one reaction, to write 

R' = W,^W, + W,-R . (15) 



90 



nh'ii)(!i<:s. 



As Iho lH\'ini is supposed to have no weii^^lit, no load will act upon 
the lK\'ini helAveen the .^ivcn weights. The bendini,^ moments, 
al li)e points of appht-alion of ilie three weights or loads will be 



M,=R{a I/O -ir,/>. 

M.,,=R{a \b\c) ir,(/' |-c)-ir,/. 



(i6) 



After substituting the value of /\ from ecjuatitm (14) in equa- 
tions (i()) the values of the latter are at onee known. 




1:1 i:iil 

il!l|llliiii| ii 
" 'Tliil'il 



Wa 



li||l|l 
III I I 
I I Mill 



S'=-R' 



Fig. 13. 

The bending produeed by eaeh weight will also be represented 
precisely like that in Fig. 12. The triangle ANB represents the 
i)ending iirodueed by \\\; AOB the bending prcxiuccd by W./, 
iind APH the bending produced by IF,. The resultant bending 
effect produced bv the three loails or weights acting sinuilta- 
neously is siniplv the summation of the three effeets each due to 
a single load. Hence IK' is erected vertically through the pcnnt 
of application oi' 11',, so as to ec]ual DN added to the two vertical 
intercepts between AJ^ and AP, and .1/:? antl AO. Similarly, 
HF is equal to IIO added to the intcrcc]->ts between AB and .4/^, 
and .4/)' and BN. Finally, KL is equal to PL added to the other 
two interce]'>ts, one between AB antl /^^'A', and the oihcv between 



SHEAR IN TERMS OF JiENDING' MOMENT. 91 

A/j (ind 110. Straight lines then arc drawn through A, C, F, K, 
and !'>. Any vertical intercept between AB and. ACFKB will 
represent the bending moment in the beam at the corresponding 
point. Obviously any number of loads of any magnitude, or 
a uniform load, may l)c treated in ])rcc'isely tlic same way. 

An important practical rule can readily b'c deduced from 
the equations (16), each one of which may be regarded as a gen- 
eral equation of moments. If the system of tlirec, or any other 
number of loads, be moved a small distance Ax, while they all 
remain separated by the same distances as before, the bending 
moment M will be changed by the amount shown in equation 
(i6a): 

AM ^ R Ax -WJx-WJx- etc. . . . (i6a) 
If the notation of the differential calculus be used by writing the 
letter d instead of A, and if, both members of equation (16a) be 
then divided by dx, equation ( 1 6/;) will result : 

AM dM ,, r,r i,r . 1 / , . 

-— = _— = /^-H/i-M^2 -etc. = shear. . (166) 

The second member of this equation shows the sum of all 
the external forces acting on one portion of the beam, that j)or- 
tion being limited by the section about which the moment M 
acts. That sum of all the external forces, as given by the second 
member of equation (166), is evidently the tc^tal transverse shear 
at the section considered. P>juation (166) then shows, in the 
language of the differential calculus, that the first derivative of 
M in respect to x is equal to the total transverse shear. Jt is 
further established in the differential calculus thcit whenever a 
function, such as M, the bending moment, is a maximum or a 
minimum, the first derivative is equal to zero. The ^ipplication 
of this principle to equation (166) shows that the bending mo- 
ment in any beam or truss has its greatest value wherever the 
shear is zero. Hence, in order to determine at what secticjn 
the V)ending moment has its greatest value in any loaded beam 
carrying a given system of loads, it is only necessary to .sum up 
all the forces or loads, including the reaction A', on that beam 
from one end to the point where that sum or shear is zero ; at 
this latter point the greatest moment sought will be found. 'J'his 



92 BRIDGES. 

is a verv simple method of deteniiiniiig the section at which the 
srreatest moment in the beam exists. 

The preceding fonnulc\? and diagrams may be extended to 
include an}^ number of loads, and they are constantly used in 
engineering practice, not only for beams and girders in buildings, 
but also for bridges canying railroad trains. ^Yhatever may 
be the number of loads, the expressions for the bending moments 
at the various points of application of those loads are to be 
wT-itten precisely as indicated in equations (i6). When the 
number of loads becomes great the number of terms in the equa- 
tions coiTespondingly increase, but in reality they are just as 
simple as those for a smaller number of loads. 

The diagram for the vertical shear in this beam is the loAver 
part of Fig. 13. As in the case of Fig. 12 the shear at A is the 
reaction R, as it is R' at the other end of the beam. The shear 
in the portion AD of the beam has the value R, but in passing 
the point D to the right the weight ]]\ represented by OT must 
be subtracted from R, so that the shear o\-er the section b of the 
span is i?-H\ or OT' in the diagi-am. Similarly, in passing the 
point H toward the right, both IF, and n\ must be subtracted 
from R, giving the negative shear (the previous shear being 
taken positive) T'TF. The negative shear MV remains constant 
throughout the distance c, but is increased by TT'3 at the point L, so 
that throughout the distance d the shear S' = -R'. These shear 
values are all sho^^'n in the lower portion of Fig. 13 by the vertical 
shaded lines. Obviously it is a matter of indifference whether 
the shear above the straight line LiJ is made positi^■e or negative ; 
it is only necessary to recognize that the signs are different. 

In the case of heavy beams, either built or rolled, as in rail- 
road structiu"es, it is of the greatest importance to detennine 
both the bending moments and the shears, as represented in the 
preceding equations and diagrams, and to provide sufficient metal 
to resist them. 

The case of Fig. 13 is perfectly general for moments and 
shears, and the methods developed are applicable to any amotmt 
or anv svstem of loading whatever. 

830 Bending Moments and Shears with Uniform Loads. — • 
Fig. 14 represents what is really a special case of Fig. 13, in which 



BENDING MOMENTS AND SHEARS WITH UNIFORM LOADS- 03 

the loading is utiiform for each unit of length of the beam through- 
out the whole span /. Inasmuch as the load is uniformly dis- 
tributed, it is evident that the reaction at each end of the beam 
will be one half the total load, or 

R=R' = ~ (17) 




Fig. 14. 



The general expression for the bending moment at any point 
G in the span, and located at the distance x from the end .4, will 
take the form 

X w 



]\I =Rx-wx.- = ~x{l-x) (18) 



This equation, giving the value of i\/, is the equation of a parabola 
with the vertex over the middle of the span. The bending 

moment at the latter point will be found by placing x = - in 



equation (18), which will give 



M = 



-,.72 



(19) 



Hence, in Fig. 14, if the vertical line DC be erected at D, so as to 
represent the value of M in equation (19) to a convenient scale, 
the parabola ACB may be at once drawn. Any vertical inter- 
cept, as GF between AB and the curve AFCB, will represent 
by the same scale the bending moment in the beam at the point 
indicated by the intercept. Equation (19), giving the greatest 
external bending moment in a simple beam due to a uniform 
load, is constantly employed in structural work, and shows that 



94 BRIDGES. 

that moment is equal to the total load multiplied by one eighth 
of the span. 

It has already been shown, in connection with Fig. 12, that 
when a single centre weight rests on a beam the centre bending 
moment is equal to that weight multiplied by one fourth the 
span. If the total uniform load in the one case is equal to the 
single load in the other, these equations show that the single 
centre load will produce just double the bending moment due 
to the same load uniformly distributed over the span. Wherever 
it is feasible, therefore, the load should be distributed rather 
than concentrated at the centre of the span. 

That portion of Fig. 14 shaded with vertical lines shows the 
shear existing in the beam. Evidently the shear at each end is 
equal to the reaction, or one half the total load on the span. The 
expression for the shear at any point, as G, distant x from A will 
be 

S = R — wx=w[ — x) (20) 



If :r = - in equation (20), 5 becomes equal to zero. In other 

words, there is no shear at the centre of the span of a beam uni- 
formly loaded. Hence, if at each end of the span a vertical line 
AK or BL be laid off downward, and if straight lines KD and 
DL be drawn, any vertical intercept, as GH, between these lines 
and AB will represent the shear at the corresponding point. 
Equation (20) also shows that the shear S at any point is equal 
to the load resting on the beam between the centre D and that 
point. Although this case of uniform loading is a special one it 
finds wide application in practical operations. 

84. Greatest Shear for Uniform Moving Load. — The preced- 
ing loads have been treated as if they were occupying fixed 
positions on the beams considered. This is not always the case. 
Many of the most important problems in connection with the 
loading of beams and bridges arise under the supposition that the 
load is movable, like that of a passing railroad train. One of the 
simplest of these problems, although of much importance, con- 
sists in finding the location of a uniform moving load, like that 
of a train of cars, which will produce the greatest shear at a given 



GREATEST SHEAR FOR UNIFORM MOVING LOAD. 95 

point of a simple beam, such as that represented in Fig. 15, in 
which a moving load is supposed to pass continuously over the 
span from the left-hand end .4 . It is required to determine what 
position of this uniform load will produce the greatest shear at 
the section C. 

R] ' c p' 

^^ [-)Oonnonnnr|^nonD Ig 

Fig. 15. 

Let the moving load extend from A to any point D to the 
right of C. The two reactions R and i?' may be found by the 
methods already indicated. Let W represent the uniform load 
resting on the portion CD of the span. The shear 5' existing 
at C will be 

S'=R'-W (21) 

Let i?'" be that part of R' which is due to W, and R" that 
part due to the load on AC. Evidently R'" is less than W ; then 

S'=R" + R"'-W (22) 

Since the negative quantity W is greater than the positive quan- 
tity R"\ S' will have its greatest value when both W and R"' 
are zero. Hence the greatest shear at the point C will exist 
when 

- S'=R'' (23) 

Obviously the loading must extend at least from A to C in 
order that R" may have its maximum value. Hence the greatest 
shear at any section will exist when the uniform load extends from 
the end of the span to that section, whatever may be the density of 
the load. 

If the segment of the span covered by the moving load is 
greater than one half the span, the maximum shear is called 
the main shear; but if that segment is less than one half the span, 
the maximum shear is called the counter -shear. The reason for 
these two names will be apparent later in the discussion of bridge- 
trusses. 

This rule for determining the maximum shear at any section 
of a beam is equally applicable to bridge-trusses under certain 
conditions, and has an important bearing upon the determination 



96 



BRIDGES. 



of the greatest stresses in some of the members of bridge-frames, 
although it has less importance now than it had in the earlier 
days of bridge building. 

85. Bending Moments and Shears for Cantilever Beams. — The 
case of a loaded overhanging beam or cantilever bracket, as shown 
in Fig. 16, is sometimes found. In that figure a single weight W 
is supposed to be applied at the end, while a uniform load w per 
unit of length extends over its length /. The bending moment 
at any point C distant x from the end will obviously be 



M = Wx + 



wx 



(24) 




Fig. 16. 

The greatest value of the bending moment will be found by 
placing X equal to / in equation (24), and it will have the value 



M,=Wl + 



.(25) 



The shear at any point and at the end .4 respectively will be 

S = W-\-wx and S^=W + n'l (26) 

The shear due to W is equal to itself and is constant throughout 

the whole length of the beam. 

The second term of the second member of equation (24) is the 

equation of a parabola with its vertex at B, Fig. 16. Hence if 

wP 
AF be laid off equal to — , and if the parabola FHB be drawn, 

any vertical intercept, as HK, between that curve and AB will 
represent the bending moment at the corresponding point. On 
the other hand, the first term of the second member of equation 
(24) shows that the bending moment due to W varies directly 



GREATEST BENDING MOMENT WITH ANY LOADING. 97 

as the distance from B. Hence if AG be laid off vertically down- 
ward from A equal to Wl to any convenient scale, then any inter- 
cept, as KL, between AB and BG will represent the bending 
moment due to VV at the corresponding point of the beam. 

86. Greatest Bending Moment with any System of Loading. — 
One of the most important positions of loading to be established 
either for simple beams or for bridge-trusses is that at which 
any given system of loading whatever is to be placed on any 
span so as to produce the maximum bending moment at any 
prescribed point in that span. In order to make the case per- 
fectly general a system of arbitrary loads, like that shown in 
Fig. 17, is assumed and the system is supposed to be a moving 
one. 



<!!^wk 



Iw- >A; >^i.^^ ^ ^^ 



(^a^b^'c-^c 






Fig. 17. 
The separate loads are placed at fixed distances apart, indi- 
cated by the letters a, b, c, d, etc., VV^ being supposed to be at 
the head of the train, while W„ is the last load having a variable 
distance x between it and the end of the span. In Fig. 1 7 this 
system of moving loads or train is supposed to pass over the 
span / from right to left. The problem is to determine the posi- 
tion of the loading, so that the bending moment at the section C 
of the beam or truss will be a maximum, the section C being at 
the distance /' from the left-hand end of the span. The com- 
plete analysis of this problem is comparatively simple and may 
readily be found, but it is not necessary for the accomplishment 
of the present purpose to give it here. In order to exhibit the 
formula which expresses the desired condition, let W,,' be that 
weight which is really placed at C, but which is assumed to be an 
indefinitely short distance to the left of that point, for a reason 
which will presently be explained. The equation of condition 
or criterion sought will then be the following : 

I w, + w,+w,-{- ... +w; • •• • • w; 

If the loads are so placed as to fulfil the condition expressed 



98 BRIDGES. 

in equation (27), the bending moment at section C will be a max- 
imum. If the variation in the train weights is very great, it is 
possible that there may be more than one position of the train 
which will satisfy that equation. It is necessary, therefore, 
frequently to try different positions of the loading by that cri- 
terion and then ascertain which of the resulting maximum 
moments is the greatest. It is not usually necessary to make 
more than one or two such trials. The application of the equa- 
tion is therefore simple and involves but little labor. 

It will usually happen that W„> in equation (27) is not to be 
taken as the whole of that weight, but only so much of it as may 
be necessary to satisfy the equation. This is simply assuming 
that any weight, W, may be considered as made up of two sepa- 
rate weights placed indefinitely near to each other, which is 
permissible. 

After having found the position of loading which satisfies 
equation (27), the resulting maximum bending moment will 
take the following form : 

M, = j[W,a+{W, + W,)h+ . . . +{W,-\-W,+ . . . +W„)x\ 

-W,a-{W,-vW,)h- . . . -{W, + W,-\- . . . -YW„,.,){1). (28) 

In this equation x corresponds to the position of loading for 
maximum bending, while the sign (?) represents the distance 
between the concentrations W„'^^ and W„'. This equation has 
a very formidable appearance, but its composition is simple and 
it is constantly used in making computations for the design of 
railroad bridges. The loads W^, W^, W^, etc., represent the 
actual weights on the driving-axles and other axles of locomo- 
tives, tenders, and cars, and the spacings a, b, c, etc., are the 
actual spacings found between those axles. In other words, 
these quantities are the actual weights and dimensions of the 
different portions of moving railroad trains. 

The computations indicated by equation (28) are not made 
anew in every instance. Concentrated weights of typical loco- 
motives, tenders, and cars are prescribed by different railroad 
companies for their different classes of trains, ranging from the 
heaviest freight traffic to the lightest passenger train. A tabu- 



APPLICATIONS TO ROLLED BEAMS. 99 

lation is then made from equation (28) for each such typical 
train, and it is used as frequently as is necessary to design a bridge 
to carry the prescribed traffic. The tabulations thus made are 
never changed for a given or prescribed loading. 

87. Applications to Rolled Beams. — It is to be remembered 
that these last observations do not limit the use of equations (27) 
and (28) to railroad-bridge trusses only; they are equally appli- 
cable to solid and rolled beams and are frequently used in connec- 
tion with their design. Great quantities of these beams and 
various rolled steel shapes are used in the construction of large 
modern city buildings, as well as in railroad and highway bridge 
structures. The steel frames of the great office buildings, so 
many of which are seen in New York and Chicago as well as in 
other cities, which carry the entire weight of the building, are 
formed wholly of these steel shapes. The so-called handbooks 
published by steel-producing companies exhibit the various 
shapes rolled in each mill. These books also give in tabular 
statements many numerical values of the moment of inertia, 
the section modulus, and other elements of all these sections, 
so that the formulse which have been established in the pre- 
ceding pages may be applied in practical work with great con- 
venience and little labor. Tables are also given showing the 
sizes of rolled beams required to sustain the loads named in 
them. Such tables are formed for practical use, so that, know- 
ing the distance apart of the beams, their span, and the load 
per square foot which they carry, the required size of beam may 
be selected without even computation. Such labor-saving 
tables are quite common at the present time, and they reduce 
greatly the labor of numerical computations. 

L.cfC. 



CHAPTER VIIL 



88. The Truss Element or Triangle of Bracing. — A number of 
the preceding formulas find their apphcations to bridge-trusses, 
as well as to beams; hence it is necessary to give attention at 
least to some simple forms of those trusses. 

The skeleton of every bridge-truss properly designed to carry 
its load is an assemblage of triangles. In other words, the truss 
element, i.e., the simplest possible truss, is the triangular frame, 
such as is shown in skeleton in Figs. i8 and i8a. These simple 
triangular frames are sometimes called the King-post Truss. 
The action of such a triangular frame in carrying a vertical load 
is extremely simple. In Fig. i8 let the weight W be suspended 










H 


\o 




R> 


Y 


^ "^- 


'f 


\^ 


,R' 


A 


/ 






\^ 


B 


'(///m 


I ^ 


1 


^ 


5: 


^^^\^ 










1 





Fig. i8a. 

from the apex C of the triangle. The line CF represents that 
weight, and if the latter be resolved into its two components 
parallel to the two upper members of the triangular frame, the 
two component forces CG and CD will result. If from D and G 
the horizontal lines DH and GO be drawn, those two lines will 
represent the horizontal components of the forces or stresses in 
the two bars CA and CB. The force HD will act to the left at 
the point A, and the force CG will act to the right at B, and as 
these two forces are equal and opposite to each other, equilibrium 
will result. Either of the horizontal forces will represent the 
magnitude of the tension in AB. Both AC and CB will be in 

100 



SIMPLE TRUSSES. 101 

compression, the former being compressed by the force CD, and 
the latter by the force CG. The manner of drawing a parallel- 
ogram of forces makes the triangle COG similar to CNB, and CHD 
similar to CNA ; hence HW divided by CH will be equal to AN 
divided by iV5. But HW is the vertical component of the 
stress in CB, while CH is the vertical component of the 
stress in AC, the latter being represented by the reaction R and 
the former by the reaction R'. It is seen, therefore, that the 
weight W is carried by the frame to the two abutment supports 
A and B, precisely as if it were a solid beam. In other words, 
the important principle is established that when weights rest 
upon a simple truss supported at each end they will produce 
reactions at the ends in accordance with the principle of the 
lever, precisely as in the case of a solid beam. In engineering 
parlance it is stated that the weight W is divided according to 
the principle of the lever,- and that each portion travels to its 
proper abutment through the members of the triangular frame. 
If the two inclined members of the triangular frame are equally 
inclined to a vertical, the case of Fig. 1 8a results, in which one half 
of the weight goes to each abutment. 

The triangular frame, with equally inclined sides, shown in 
Fig. 1 8a, is evidently the simplest form of roof -truss, constituting 
two equally inclined members with a horizontal tie. 

89. Simple Trusses. — The simplest forms of trussing used for 
bridge purposes are those shown in Figs. 19, 20, and 21. There 
are many other forms which are exhibited in complete treatises 
on bridge structures, but these three are as simple as any, and 
they have been far more used than any other types. The hori- 
zontal members af and AB are called the "chords," the former 
being the upper chord and the latter the lower chord. The 
vertical and inclined members connecting the two chords are 
called the web members or braces. When a bridge is loaded, 
either by its own weight only, or by its own weight added to 
that of a moving train of cars, the upper chord will evidently 
be in compression, while the lower chord is in tension. A por- 
tion, which may be called a half, of the web members will be in 
tension and the other portion, or half, will be in compression. 

The function of the upper and lower chords is to take up or 



102 BRIDGES. 

resist the horizontal tension and compression which correspond 
to the direct stresses of tension and compression existing in the 
longitudinal fibres of a loaded solid or flanged beam. The metal 
designed to take these so-cahed direct stresses is concentrated 
in the chords of trusses, whereas it is distributed throughout the 
entire section of a beam, whether that beam be solid or flanged. 
The function of the web members of a truss is to resist the trans- 
verse or vertical shear which is represented by the algebraic sum 
of the reactions and loads. The total section of a solid beam 
resists these vertical shears, while the web only of a flanged beam 
is estimated to perform that duty. The horizontal shears, which 
have already been recognized as existing along the horizontal 
planes in a bent beam, are resisted by the inclined web members 
of a truss, the horizontal stress components being the horizontal 
shears, whereas the vertical shears are resisted by the vertical 
web members of a truss. If the web members are all inclined, 
as shown in Fig. 21, each web member resists both horizontal 
and vertical shear. It is thus seen that the members of a truss 
perform precisely the same duties as the various portions of 
either solid or flanged beams. Inasmuch as the chords of bridge- 
trusses resist the direct or horizontal stresses of tension and com- 
pression produced by the bending in the truss, it is obvious that 
the greatest chord stresses will be found at the centre of the 
span, and that they will be the smallest at the ends of the span. 
In the web members, on the contrary, since the vertical shear 
is the greatest at the ends of the span and equal to the reactions 
at those points, decreasing towards the centre precisely as in 
solid beams, the greatest web stresses will be found at the ends 
of the span and the least near the centre. It is obvious that the 
areas of cross-sections of either chords or web members must 
be proportioned to the stresses which they carry. Hence the 
distribution of stresses just described tends to a uniform distri- 
bution of the truss weights over the span. 

90. The Pratt Truss Type. — In the discussion of these three 
simple types of trusses, the simplest possible loading of a perfectly 
uniform train will be assumed. The portions into which the trusses 
are divided by the vertical or inclined bracing are called panels. 
In Fig. 19, for instance, the points i, 2, 3, 4, 5, and 6 of the lower 



THE PRATT TRUSS TYPE. 103 

chord and a, b, c, d, e, and / of the upper chord are cahed panel- 
points. The distance between each consecutive two of these 
points is cahed a panel length. The uniform train-load which is 
to be assumed will be represented by the weight W at each panel- 
point. This is called the "moving load" or "live load." The 
own weight of the structure is called the ' ' dead load ' ' or the 
"fixed load." The dead load per upper-chord panel will be 
taken as W, and W\ for the lower chord. The loads to be used 
will, therefore, be as follows: 

Panel moving load = W ; 

Upper-chord panel dead load = W ; 
Lower " " " " =W,. 

There will also be used the length of panel and depth of truss as 
follows : 

Panel length =p; 

Depth of truss = c/. 

In these simple trusses with horizontal upper and lower chords 
the stress in any inclined web members is equal to the shear 
multiplied by the secant of the inclination of the members to a 
vertical line. Also, at each panel -point every inclined web mem- 
ber, in passing from the end to the centre of the span, adds to 
either chord stress at that point an amount represented by the 
horizontal component of the stress which it carries ; or, what is 
the same thing, an amount equal to the shear at the panel in 
question multiplied by the tangent of its angle of inclination to 
a vertical line. 

It has already been shown in discussing solid beams that the 
greatest shear at any section will be found when the uniform 
moving load covers one of the segments of the span. This 
principle holds equally true for trusses carrying uniform panel- 
loads like those under consideration. In determining the stresses 
in these trusses, therefore, the inclined w^eb members will take 
their greatest stresses when the moving train or load extends 
from the farthest end of the span up to the foot of the member 
in question. In this connection it is to be observed also that 
any two web members meeting in the chord which does not carry 



104 



BRIDGES. 



the moving load take their greatest stresses for the same posi- 
tion of the latter. The so-called "counter web members" take 
no stresses from the dead load. 

Inasmuch as every load placed upon a truss will produce com- 
pression in the upper chord and tension in the lower, the greatest 
chord stresses will obviously exist when the moving load covers 
the entire span, and that condition of loading is to be used for 
the stresses in the following cases. 

Bearing these general observations in mind, the ordinary sim- 
ple method of truss analysis yields the tabulated statement of 
stresses given below for the three types selected for consideration. 
The first case to be treated is that of Fig. 19, which represents 
the Pratt truss type. The moving load is supposed to pass 
across the bridge from right to left. The plus sign indicates 
tension and the minus sign compression. 



a Ui & U2 c U3 d 




^^^ Li 6 L2 5 L3 4 L, 

Fig. 19. 



Stress in c^ 
Stress in T ^ 

( ( i i n-^ 

^ 3 

a I I 'J' 



+ (i + DFTsec a=\W sec a. 
+ (l + f + f)Frsec a=-|iy sec a; 
+ [(i + -| + T + 4)^ + W'' + ^i]seca 
(j.oW + VF' + Vrjseca; 

+ [(T + T + f + f + 4)l^+2w' + 2wJseca 
= (J/W + 2w' + 2 wj sec a ; 

Stress in P3 = - (f VT + W) ; 

" " P, = -2>iW + W' + W,)sQca. 

Stress in L^ = Stress in L^= -\- t,{W -{-W + W^) tan a ; 
L,= " " L2 +2(W + Vr' + M/J tana 

= +5(W + T^' + T^J tana; 
L,= '' " L3 +{W + W' + W,)ts.na 

= +6(I^ + W' + WJtana. 



( ( it 



< ( ( ( 



( ( ( < 



THE HOWE TRUSS TYPE. 



105 



Stress in 17^^ = — Stress in L^ 






L, 

U. 



■6(W + W' + W^)tana. 



It is easy to check any of the chord stresses by the method 
of moments. As an example, let moments first be taken about 
the panel-point 5 in the lower chord, and then about the panel- 
point c in the upper chord. The following expressions for the 
chord members U^ and L^ will be found, and it will be noticed 
that they are identical with the stresses for the same members 
given in the preceding tabulation, the counter-members, shown 
in broken lines, being omitted from consideration as they are not 
needed. 

stress in U.^^^f^S^'^+^^+mP 

a 

= S(.W + W' + W,)^ = SiW + W' + W,) t&n a. . (29) 
Stress in ^^^R-SP- ^(W + W + WJ ..jp 

= 6{W + W' + W,)tana (30) 

Q . 

U2 c Ua d e \ f 




Fig. 20. 

91. The Howe Truss Type. — The truss shown in Fig. 20 is 
the skeleton of the Howe truss, to which reference has already 
been made. The inclined web members are all in compression, 
while the vertical web members are all in tension. In the Howe 
truss all compression members are composed of timber. It has 
the disadvantage of subjecting the longest web members to 
compression. It thus makes the truss, if built all in iron or 
steel, heavier and more expensive than the trusses of the Pratt 
type. As in the preceding case, the moving train or load is 
supposed to pass across the bridge from B to A. Also, as before, 
the + sign indicates tension and the — sign compression. The 



106 BRIDGES. 

greatest stresses, given in the tabulated statement below, can 
be computed or checked by the method of moments in this case, 
precisely as in the preceding. 

Stress in c^ = - {\ + ^)W sec a= - \W sec a. 
Stress in P, = - {\-\-^ + ^)W sec a = -fW sec a; 

" " P^=- GVW + W + H^i) sec a; 

" " p^ = - {lAW + 2 W + 2 WJ sec a ; 

" '' P^ = -2>{W + W' + W;)seoa. 

Stress in T^= + {\^-W + W^) sec a ; 

" '' T^ = + {sW + 2W' + 3W,) sec a. 

Stress in L, = +3(W + W' + W^) tan a ; 
" " L^= -{- ^(W + W' + W,) tan a+2{W + W' + W,) tan a 

= + SOV + W' + Wi) tana; 
" " L3 = + 5(W + W' + Vrj tan a+CVF + M/' + T^i) tana 

^ +6(1^ + 1^' + V^i) tana; 
" " L^ = Stress in L^. 
Stress in U^ = — Stress in L^ ; 
" " [/,= - " " w. 

It will be noticed in the cases of Figs. 19 and 20 that upper 
and lower chord panels in the same lozenge or oblique panel have 
identically the same stresses, but with opposite signs. For 
instance, in Fig. 20 the stress in U^ is equal in amount to that 
in L^; and the same observation can be made in reference to 
the stresses in U^ and L^ of Fig. 19. This must necessarily 
always be the case in trusses having vertical web members. 

In making computations for these forms of trusses it is very 
essential to observe where the first counter-member, as c^, must 
be used. These counter-members may be omitted if the proper 
main web members near the centre of the span are designed to 
take both tension and compression. 

92. The Simple Triangular Truss. — The truss shown in Fig. 
21, in which all the web members have equal inclination to a 
vertical line, is sometimes called the Warren Truss, although 
that term has also been applied specially to this type of truss 



THE SIMPLE TRIANGULAR TRUSS. 107 

SO proportioned as to make the depth just equal to the panel 
length. As before, the moving train is supposed to pass over 
the bridge from B toward A , while the + sign represents tension 
and the — sign compression. The greatest stresses are the 
following. 



a Ui 6 Us c Us d 


9 


^'r 


-p- 


i/ 




ff 




/ \/- \=A VA / 


\/ 


/ 


I 


/\ 


^ 

^ 


A 


\b 


*i^| Li 6 La 5 L3 4 U 
S 


3 




2 




1 




mss 



Stress 
( < 


in 


P.= 

Ps- 

p^ = 
p,= 



Fig. 21. 

( -(^W + W') sec a, or 

( - (ipvr+ 1^17' + Ty,) sec a, or 
\ +{^W-iiW'-W^)seca; 
- (mV + 2iW' + 2 Vrj sec a ; 
-(3W^ + 3W + 3^i)seca. 

5/r^55m r - ( +(V-^ + W + T^g sec a, or 

" " T^= + {i^'-W+iiW' + 2W,)seca; 
" " r,= + (3^ + 21]^' + 31^ J sec a. 
Stress in L^ = + 3 (I'F + VF' + T^,) tan a + iTF' tan a ; 
" " ^2 = ^^''^^•^ ^'^ L, + (5IF + 5 VT' + 5 VF,) tan a 

= +8(M^+M/' + l^,) tan a + iH^' tan a; 
" " L3 = 5tr^55 ^'w L^ + 3 (H^ + H'^' + Ty,) tan a 

= + ii{W-\-W' + W;) tan a + iH'' tan a; 
" " L, = 5^r^55 i;i L,+ {W + W' + W^) tan a 

= + i2{W + W'-\-W,) tan a + W tan a. 

Stress in U^ = -6(W + W'i-W,) tan a ; 
" " u^ = -6(W + W' + W,)tcina-4iW + W + M\) tan a 

' = -io(W + W' + W,)tsina; 
" " U, = - io(W + W' + W,) tan a-2(W + W' + W,) tan a 
= -i2(H'^ + T^^' + H^i) tana. 

The chord stresses may be checked or found by the method 
of moments, precisely as in the case of Fig. 19. If, for instance, 
it is desired to determine the stresses in the upper chord member 



108 



BRIDGES. 



U^, moments must be taken about the lower-chord panel-point 5, 
and about the upper- chord panel-point d for the lower- chord 
stress in L^. Taking moments about those points, results given 
in equations (31) and (32) will at once follow, which it will be 
observed are identical with the values previously found for the 
same members. 



Stress in U^ 



Stress in L, = + 



{ ^W + ZW + ZW ,) .2 p- 2W'p- {W -\-W ,)p 

d 
io{W + W' ^V[\) l^n a (31) 



d 



^- 1 2 (FT + VT, + PF') tan a + il^' tan a. 



(32) 



93. Through and Deck Bridges. — These simple trusses have 
all been taken as belonging to the * * through" type, i.e., the mov- 
ing load passes along their lower chords. It is quite common to 
have the moving load pass along the upper chords, in which cases 
the bridges are said to be "deck" structures. The general 
methods of computation are precisely the same whether the 
trusses be deck or through. It is only necessary carefully to 
observe that the application of the methods of analysis depends 
upon the position of each panel-load as it passes across the struc- 
ture. 

94. Multiple Systems of Triangula tion. — Figs. 19, 20, and 21 
exhibit what are called single systems of triangulation or single 




Fig. 22. 

systems of bracing, but in each of those types the system of web 
members may be double or triple ; in other words, they may be 
manifold. There have been many bridges built in which two 
or more systems of bracing are employed. Fig. 22 represents 
a truss with a double system of triangulation, known at one time 



INFLUENCE OF MILL AND SHOP CAPACITY. 



109 



as the Whipple truss. Fig. 23, again, exhibits a quadruple 
system of triangulation with all inclined web members. The 




Fig. 23. 

method of computation for such manifold systems is precisely 
the same as for a single system, each system in the compound 
truss being treated as carrying those loads only which rest at its 
panel points. This procedure is not quite accurate. The com- 
plete consideration of an exact method of computation would 
take the treatment into a region of rather complicated analysis 
beyond the purposes of these lectures, but its outlines will be 
set forth on a later page. The exact method of treatment of 
two or more web systems involves the elastic properties of the 
material of which the trusses are composed. In the best mod- 
em bridge practice engineers prefer to design trusses of all 
lengths with single web systems, although the panels are fre- 
quently subdivided to avoid stringers and floor-beams of too 
great weight. 

95. Influence of Mill and Shop Capacity on Length of Span. — 
In the early years of iron and steel bridge building the sizes of 
individual members were limited by the shop capacity for hand- 
ling and manufacturing, and by the relatively small dimensions 
of bars of various shapes, and of plates which could be produced 
by rolling-mills. As both mill and shop processes have advanced 
and their capacities increased, corresponding progress has been 
made in bridge design. Civil engineers have availed themselves 
of those advances, so that at the present time single-system 
trusses with depths as great as 85 feet or more and spans of over 
550 feet are not considered specially remarkable. 

96. Trusses with Broken or Inclined Chords. — As the lengths 
of spans have increased certain substantial advantages have been 
gained in design by no longer making the upper chords hori- 



110 



BRIDGES. 



zontal in the case of long through-spans, or indeed in the cases 
of through-spans of moderate length. The greatest bending 
moments and the greatest chord stresses have been shown to 
exist at the centre of the span, while the greatest web stresses 
are found near the ends. Trusses may be lightened in view of 
those considerations by making their depths less at the ends than 
at the centre. This not only decreases the sectional areas of the 
heaviest web members near the ends of the truss, but also shortens 
them. It adds somewhat to the sectional area of the end upper- 
chord members, but the resultant effect is a decrease in total 
weight of material and increased stability against wind pressure 
by the decreased height and less exposure near the ends. It 
has therefore come to be the ruling practice at the present time 
to make through -trusses with inclined upper chords for prac- 
tically all spans from about 200 feet upward. A skeleton dia- 
gram of such a truss is given in Fig. 24. 



A 




Fig. 24. 

97. Position of any Moving Load for Greatest Web Stress. — 

In the preceding treatment of bridge-trusses with parallel and 
horizontal chords a moving or live load has been taken as a 
series of uniform weights concentrated at the panel-points. 
This simple procedure was formerly generally used, and at 
the present time it is occasionally employed, but it is now 
almost universal practice to assume for railroad bridges a 
moving load consisting of a series of concentrations, which 
represent both in amount and distribution the weights on the 
axles of an actual railroad train. If a bridge is supposed to be 
traversed by such a train, it becomes necessary to determine 
a method for ascertaining the positions of the train causing 
the greatest stresses in the various members of the bridge-truss. 
The mathematical demonstration of the formulae determining 



CRITERIONS FOR BOTH CHORD AND WEB STRESSES. HI 

those positions of loading need not be given here, but it can be 
found ill almost any standard work on bridges. 

In order to show concisely the results of such a demonstration 
let it be desired to find the position of a moving load which will 
give the greatest stress to any web member, 'as 5 in Fig. 24. Let 
the point of intersection of GK and DC be found in the point 0, 
then let CKhe extended, and on its extension let the perpendic- 
ular h be dropped from 0. The distance of the point from A, 
the end of the span, is i, while m is the distance AD. Using the 
same notation which has been employed in the discussion of 
beams, together with that shown in Fig. 24, equation (33) ex- 
presses the condition to be fulfilled by the train-loads in order 
that 5 shall have its greatest stress. The first parenthesis in 
the second member of that equation represents the load between 
the panel p and the left end of the span, while the second 
parenthesis represents the load in panel p itself. 

W, + W,+ ... +W„=--.(W, + W.,+ etc.) 

pi 

It will be noticed in equation (33) that the quantity m shows 
in what panel the inclined web member whose greatest stress 
is desired is located, and it is important to observe that panel 
carefully. If, for instance, the vertical member KD were in 
question, the point would be located at the intersection of 
the panel A^/\ and the lower chord of the bridge. In other words, 
the point O must be at the intersection of the two chord mem- 
bers belonging to the same panel in which the web member is 
located. 

98. Application of Criterions for both Chord and Web Stresses. 
— The criterion, equation (t,^), belongs to web members only. 
If it is desired to find the position of moving load which will give 
the greatest chord stresses in any panel, equation (27), already 
established for beams, is to be used precisely as it stands, the 
quantity /' representing the distance from one end of the span 
to the panel-point about which moments are taken. 



112 BRIDGES. 

If the desired positions of the moving load for greatest 
stresses have been found by equations (27) and (33), those 
stresses themselves are readily found by taking moments about 
panel-points for chord members and about the intersection- 
points 0, Fig. 24, for web members. These operations are simple 
in character and are performed with great facility. Tabulations 
and diagrams are made for given systems of loading by which 
these computations are much shortened and which enable the 
numerical work of any special case to be performed quickly 
and with little liability to error. These tabulations and dia- 
grams and other shortening processes may be found set forth 
in detail in many publications and works on bridge structures. 
They constitute a part of the office outfit of civil engineers en- 
gaged in structural work. 

The criterion, equation (27), for the greatest bending mo- 
ments in a bridge is applicable to any truss whatever, whether 
the chords are parallel or inclined, but it is not so with equation 
(t,s)- I^ the chords of the trusses are parallel, the quantity i 
in equation {t,t,) becomes infinitely great, and the equation takes 
the following form : 

W, + W,+ ...+W„ = kw, + W, + etc.). . . (34) 
P 

Ordinarily the span / divided by the panel length p is equal to 
the number of panels in the span. Hence equation (34) shows, 
in the case of parallel or horizontal chords, that when the moving 
load is placed for the greatest web stress in any panel, the total 
load on the bridge is equal to the load in that panel multiplied 
by the total number of panels. 

99. Influence Lines. — A graphical method, known as that of 
"influence lines," is used for determining the greatest shears 
and bending moments caused by a train of concentrated 
weights passing along a beam or bridge-truss. Obviously it 
must express in essence that which has already been shown by 
the formulas which determine positions of moving loads for the 
greatest shears and bending moments. In reality it is the appli- 
cation of graphical methods which have become so popular to 
the determination of the greatest stresses in beams and bridges. 



INFLUENCE LINES FOR MOMENTS. 



113 



100. Influence Lines for Moments both for Beams and Trusses. 

— It is convenient to consti-uct these influence lines for an arbi- 
trary load which may be considered a unit load; the effect of 
any other load will then be in proportion to its magnitude. The 
results determined from influence lines drawn for a load which 
may be considered a unit can, therefore, be made aA^ailable for 
other loads by multiplying the former by the ratio between 
any desired load and that for which the influence lines are found. 




Fig. 25. — Bending Moment in a Simple Beam. 

AB in Fig. 25 represents a beam simply supported at each 
end, so that any load g resting upon it will be divided between 
the points of support, according to the law of the lever. Let 
it be desired to determine the bending moment at the section X 
produced by the load g in all of its positions as it passes across 
the span from A to B. Two expressions for the bending moment 
must be written, one for the load g at any point in AX, and the 
other for the load at any point in BX. The expression for the 
first bending moment is 



and that for the latter 



M=gj(l-x), 



M'-i-^x. 



(a) 



As shown in the figure, z and x, the latter locating the section 
at which the bending moments are to be found, are measured 
to the right from A. Equation (a) shows that if the quantity 
g{l-x) be laid off, by any convenient scale, as BK at right angles 
to AB, XC will represent the moment AI by the same scale when 
x=z or when z has any value between o and x. Similarly will 



114 BRIDGES. 

AD be laid off at right angles to ^S by the same scale as before, 
to represent gx. Then when x =z the expression for M' will have 
the same value XC as before. Hence if the lines AC and CB 
be drawn as parts oi AK and DB, any vertical intercept between 
AB and ACB will represent the bending at X produced by the load 
g when placed at the point from which the intercept is drawn. 
The lines AC and CB are the influence lines for the bending 
moments produced by the load g in its passage across the span 
AB. It is to be observed that the influence lines are continuous 
only when the positions of the moving load are consecutive. In 
case those positions are not consecutive the influence lines are 
polygonal in form. 

If there are a number of loads g resting on the span at the 
same time, the total bending moments produced at X will be 
found by taking the sum of all the vertical intercepts between 
AB and ACB, drawn at the various points where those loads 
rest. The influence lines drawn for a single load, therefore, may 
be at once used for any number of loads. 

The load g is considered as a unit load. If the vertical inter- 
cepts representing the bending moments by the scale used are 
themselves represented by y, and if W represent any load what- 
ever, the general expression for the bending moment at X, pro- 
duced by any system of loads, will be 

-:EWy (c) 

g 

If this expression be written as a series, the general value of the 
bending moment will be the following: 

M = ~(W,y, + W,y, + W,y, + etc.) (d) 

o 

The effect of a moving train upon the bending moment at 
any given section is thus easily made apparent by means of 
influence lines. It is obvious that there will be as many influence 
lines to be drawn as there are sections to be considered. In the 
case of a tniss-bridge there will be such a section at every panel - 
point. 

A slight modification of the preceding results is to be made 



INFLUENCE LINES FOR SHEARS. 115 

when the loads are apphed to the beam or truss at panel-points 
only. 

In Fig. 25 let i, 2, 3, 4, 5, 6, and 7 be panel-points at which 
loads are applied, and let the load g be located at the distance 
^' to the right of panel-point 5, also let the panel length be p. 

p 0' 2' 

The reactions at 5 and 6 will then be R^=g- and RQ=g—. 

P P 

l — z 
The reactions at A will then be R=g-j- . Hence the moment 

at any section A' in the panel in question will be 

M=Rx~R,iz'-{z-x})=g\^^''z-iz-z' + p-x)t]^. . (e) 

Remembering that z — z' is a constant quantity, it is at 
once clear that the preceding expression is the equation of a 
straight line, with M and z or z' the variables. If z^ =0, equation 
(e) becomes identical with equation (a), while ii z' =p, it becomes 
identical with equation (b). Hence the influence line for the 
panel in which the load is placed, as 5-6, is the straight line KL. 
It is manifest that when the load g is in any other panel than 
that in which the section A' is located, the effect of the two reac- 
tions at the extremities of that panel will be precisely the same 
at the section as- the weight itself acting along its own line of 
action. Hence the two portions AK and BL of the influence 
line are to be constructed as if the load were applied directly to 
the beam or truss, and in the manner already shown. The com- 
plete influence line will then be AKLB, and it shows that the 
existence of the panel slightly reduces the bending at any section 
within its limits. The panel 5-6, as treated, is that of a beam 
in which the bending moment will, in general, vary from point 
to point. li AB were a truss, however, X would always be 
taken at a panel-point, and no intercept between panel-points, 
as 5 and 6, would be considered. 

10 1. Influence Lines for Shears both for Beams and Trusses. — 
The influence lines for shears in a simple beam, supported at each 
end, can be drawn in the manner shown in Fig. 25a. In that 
figure AB represents a non-continuous beam with span / sup- 



116 



BRIDGES. 



ported at each end and a conventional load g at the distance z 
from A. The reaction at A will be 

l-z 

G 



R = 




Fig. 25a. — Shear in a Simple Beam. 

Let X be the section at which the shear for various positions 
of g is to be found. When g is placed at any point between A 
and X the shear 5 at the latter point will be 



S = R 



z _ 
'I' 



(/) 



but when the load is placed between B and X the shear becomes 



S'=R=g-^ 



l 



Qi) 



Obviously these two values of the shear are equations of two 
parallel straight lines, that represented by equation (/) passing 
through A , and that represented by equation (h) passing through 
B, the constant vertical distance between them being g. Hence 
let BF be laid off negatively downward and AG positively up- 
ward, each being equal to g by any convenient scale. The ordi- 
nates drawn from the various positions i, 2, t, ... 6 oi g on AB 
to AD and BC will be the shears at X produced by the load g 
at any point of the span, and determined by equations (/) and (h). 
The influence line, therefore, for the section X will be the broken 
line ADCB. When g is at X the sign of the shear changes, since 
the latter passes through a zero value. 

If a train of weights W^, W^, W^, etc., passes across the span, 
the total shear at X will be found by taking the sum of the vertical 



INFLUENCE LINES FOR SHEARS. 117 

intercepts between AB and ADCB, drawn at the positions occu- 
pied by the various single weights of the train. If those single 
weights are expressed in terms of the unit load g, the shear 5 
will have the value 

g 

y being the general value of the intercept between AB and the 
influence line. The latter shows that the greatest negative 
shear at A' will exist when the greatest possible amount of loading 
is placed on AX only, while the greatest positive shear at the 
same section will exist when BX only is loaded. If BX is the 
smaller segment of span, the latter shear is called the ' ' counter- 
shear, ' ' and the former the ' ' main shear. ' ' 

If the loads are applied at panel-points of the span only, the 
treatment is the same in general character as that employed for 
bending moments. In Fig. 25a let 4 and 5 be the panel-points 
between which the load g is found, and let the panel length be p. 
Also, let 2' be the distance of the weight g from panel-point 4. 
The reactions at ^4 and 4 will then be 

R = ~r~g and R^ = ^^-^g. 
i p 

The shear at the section A' for any position of the weight g will 
then be 

S^R-R,-,{f^^\) (k) 

As this is the equation of a straight line, with 5 and z or z' 
for the coordinates, the influence line for the panel in which the 
section A is located will be the straight line represented by KL 
in Fig. 25a. 

If z' is placed equal to o and p successively, then will equa- 
tion (k) become identical with equations (/) and Qi) in succession. 
The shears at points 4 and 5 will therefore take the same values 
as if the loads were applied directly to the beam. For the reasons 
stated in connection with the consideration of bending moments, 
loads in other panels than that containing the section for which 
the influence line is drawn will have the same effect on that sec- 



118 BRIDGES. 

tion as if they were applied directly to the beam or truss. Hence 
AKLB is the complete influence line for this case. 

It is evident that there must be as many influence lines drawn 
as there are sections to be discussed. Also, if g is taken as some 
convenient unit, i.e., looo or 10,000 pounds, it is clear that the 
labors of computation will be much reduced. 

102. Application of Influence-line Method to Trusses. — In con- 
sidering both the bending moments and shears when the loads 
are applied at panel-points, it has been assumed, as would be 
the case in an ordinary beam, that the bending moments as well 
as the shears may vary in the panel; but this latter condition 
does not hold in a bridge-truss. Neither bending moment nor' 
shear varies in any one panel. Yet the influence lines for mo- 
ments and shears are to be drawn precisely as shown in Figs. 25. 
and 25a. The section X will always be found at a panel- point, 
and no intercept drawn within the limits of the panel adjacent 
to that section carrying the load g is to be used. This method 
will be illustrated by the aid of Fig. 256. 

The employment of influence lines may be illustrated by 
determining the moment and shear in a single section of the: 
truss shown in Fig. 24, which is reproduced in Fig. 25c, when 
carrying the moving load exhibited in Fig. 256, although its use. 
may be much extended beyond this simple procedure. 

The moving load shown in Fig. 256 is that of a railroad train 
consisting of a uniform train-load of 4000 pounds per linear foot 
drawn by two locomotives with the wheel concentrations shown ;. 
it is a train-load frequently used in the design of the heaviest 
class of railroad structures. If the criterion of equation (27) be 
applied to this moving load, passing along the truss shown in 
Fig. 25c, from left to right, it will be found that the greatest- 
bending moment is produced at the section Q when the second 
driving-axle of the second locomotive is placed at the truss sec- 
tion in question, as shown in Fig. 25 c. 

The unit load to be used in connection with the influence 
lines will be taken at 10,000 pounds. Remembering that the 
panel lengths are each 30 feet, it will be seen that the panel-point 
Q is 150 feet from A. Hence the product gx will be 1,500,000 
foot-pounds. Similarly the product g{l — x) will be 900,000 foot- 



INFLUENCE-LINE METHOD FOR TRUSSES. 



119 



pounds. Laying off the first of these quantities, as ^D, at a scale 
of 1,000,000 foot-pounds per linear inch, and the second quantity, 
as BK, by the same scale, the influence line ACB can at once be 
completed. Vertical lines are next to be drawn through the 
positions of the various weights, including one through the centre 
of the uniform train-load no feet in length resting on the truss. 
The vertical line through the centre of the uniform train-load 
is shown at 0. By carefully scaling the vertical intercepts be- 
tween AB and ACB, and remembering that each of the loads 
on the truss must be divided by 10,000, the following tabulated 
statement will be obtained, the sum of the intercepts for each 
set of equal weights being added into one item, and all the 
items of intercepts being multiplied by 1,000,000: 

DO = 8,580,000 foot-pounds. 

= 4,628,000 

= 8,560,000 

= 970,000 

= 3,965,000 

= 3,600,000 

= 240,000 



.195X110 > 


:.4X 


1.78 X 


2.6 


X 


2.14 X 


4 


X 


.485 X 


2 


X 


I-525X 


2.6 


X 


.9 X 


4 


X 


.12 X 


2 


X 



2)30>543.ooo 



Moment for one truss = 15,271,500 " 

The lever-arm of ef, i.e., the normal distance from Q to ef, 
is 39.7 feet. Hence the stress in ef is 



15,271,500 
39-7 



384,700 pounds. 



All the chord stresses can obviously be found in the same manner. 
In order to place the same moving load so as to produce the 
greatest shear at the same section Q, the criterion of equation i;^^) 
must be employed. The dimensions of the truss shown in con- 
nection with Fig. 29 give the following data to be used in that 
equation: -^' = 210 feet, m = 6o feet, and ^ = 30 feet. Hence 



l(m-\-i) 
pi 



= IOy, 






Introducing these quantities into equa- 



tion (33), and remembering that the train moves on to the bridge 



120 



BRIDGES. 



from A, it would be found that the second axle of the first 
locomotive must be placed at the section Q, as shown m Fig. 
2 5(i, which exhibits the lower-chord panel-points numbered 
from I to 7. The conventional unit load g will be taken in this 
case at 20,000 pounds. It is represented as AG and BF (Fig. 




Fig. 25^. 



Qp-. 




Fig. 25^. 

25(^), laid off at a scale of 10,000 pounds per inch. K is imme- 
diately under panel-point 5 and L is immediately above panel- 
point 6, hence the broken line AKLB is the influence line desired. 
The vertical lines are then drawn from each train concentration 
in its proper position, all as shown, including the vertical line 
through the centre of the 54 feet of uniform train -load on the 
left. The summation of all the vertical intercepts between AB 
and the influence line AKL, having regard to the scale and to 



INFLUENCE-LINE METHOD FOR TRUSSES. 



121 



the ratio between the various loads and the unit load g, will 
give the following tabular statement: 

.22X54X .2X10,000= 23,760 pounds. 



2.2 X 


1.3X " 


= 28,600 


3.02 X 


2 X ' 


= 60,400 


•9 X 


I X ' 


= 9,000 


4.06 X 


I.3X ' 


= 53,780 


4.53X 


2 X ' 


= 90,060 


•5 X 


I X ' 


= 5,000 



2)270,600 



Shear for one truss =135,300 

These simple operations illustrate the main principles of the 
method of influence lines from which numerous and useful exten- 
sions may be made. 



CHAPTER IX. 

103. Lateral Wind Pressure on Trusses.: — The duties of a 
bridge structure are not confined entirely to the supporting of 
vertical loads. There are some horizontal or lateral loads of 
considerable magnitude which must be resisted; these are the 
wind loads resulting from wind pressure against both structure 
and moving train. In order to determine the magnitudes of 
these loads it is assumed in the first place that the direction of 
the wind is practically or exactly at right angles to the planes of 
the trusses and the sides of the cars. This assumption is essen- 
tially correct. There is probably nothing else so variable as both 
the direction and pressure of the wind. These variations are 
not so apparent in the exposure of our bodies to the wind, for 
the reason that we cannot readily appreciate even considerable 
changes either in direction or pressure. As a matter of fact 
suitable measuring apparatus shows that there is nothing steady 
or continued in connection with the wind unless it be its incessant 
variability. Its direction may be either horizontal or inclined, 
or even vertical, while within a few seconds its pressure may vary 
between wide limits. Under such circumstances the wind is 
as likely to blow directly against both bridge and train as in any 
other direction, and inasmuch as such a condition would subject 
the structure to its most severe duty against lateral forces, it is 
only safe and proper that the assumption should be made. The 
open work of bridge-trusses enables the wind to exert practically 
its full pressure against both trusses of a single-track bridge, or 
against even three trusses if they are used for a double-track 
structure. Hence it is customary to take the exposed surface 
of bridge-trusses as the total projected area on a plane through- 
out the bridge axis of both trusses if there are two, or of three 

123 



LATERAL WIND PRESSURE ON TRUSSES. 123 

trusses if there are three. Inasmuch as the floor of a bridge 
from its lowest point to the top of the rails or other highest point 
of the floor is practically closed against the passage of the wind, 
all that surface between the lowest point and the top of the 
rail or highest floor-member is considered area on which wind 
pressure may act. 

Many experimental observations show that on large surfaces, 
greater perhaps than 400 or 500 square feet in area, the pressure 
of the wind seldom exceeds 20 or 25 pounds per square foot, 
while it may reach 80 or 90 pounds, or possibly more on small 
surfaces of from 2 to 40 or 50 square feet in area. This dis- 
tinction between small and large exposed areas in the treat- 
ment of wind pressures is fundamental and shpuld never be 
neglected. 

This whole subject of wind pressures has not yet been brought 
into a completely definite or well-defined condition through lack 
of sufficient experimental observations, but in order to be at 
least reasonably safe civil engineers frequently, and perhaps 
usually, assume a wind pressure acting simultaneously on both 
bridge and train at 30 pounds per square foot of exposed surface 
and 50 pounds per square foot of the total exposed surface of a 
bridge structure which carries no moving load. This distinction 
arises chiefly from the fact that a wind pressure of 30 pounds 
per square foot on the side of many railroad trains, particularly 
light ones, will overturn them, and it would be useless to use a 
larger pressure for a loaded structure. There have been wind 
pressures in this country so great as to blow unloaded bridges 
ofT their piers ; indeed in one case a locomotive was overturned 
which must have resisted a wind pressure on its exposed surface 
of not less than 90 pounds and possibly more than 100 pounds 
per square foot. 

The consideration of wind pressure is of the greatest impor- 
tance in connection with the high trusses of long spans, as well as 
in long suspension and cantilever bridges, and in the design of 
high viaducts, all of which structures receive lateral wind pres- 
sures of great magnitude. 

Some engineers, instead of deducing the lateral wind loads 
from the area of the projected truss surfaces, specify a certain 



124 BRIDGES. 

amount for each linear foot of span, as in " The General Specifica- 
tions for Steel Railroad Bridges and Viaducts ' ' by Mr. Theodore 
Cooper it is prescribed that a lateral force of 150 pounds for each 
foot of span shall be taken along the upper chords of through- 
bridges and the lower chords of deck-bridges for all spans up to 
300 feet in length; and that for the same spans a lateral force 
of 450 pounds for each foot of span shall be taken for the lower 
chords of through-spans and the upper chords of deck-spans, 300 
pounds of this to be treated as a moving load and as acting on a 
train of cars at a line 8yV feet above the base of rail. 

When the span exceeds 300 feet in length each of the above 
amounts of load per linear foot is to be increased by 10 poimds 
for each additional 30 feet of span. 

Special wind-loadings and conditions under which they are 
to be used are also prescribed for viaducts. 

These wind loads are resisted in the bridges on which they 
act by a truss formed between each two upper chords for the 
upper portion of the bridge, and between each two lower chords 
for the lower portion of the structure. 



A^- 



N M 



Fig. 26. 

104. Upper and Lower Lateral Bracing. — Fig. 26 shows what 
are called the upper and lower lateral bracing for such trusses as 
are shown in the preceding figures. The wind is supposed to 
act in the direction shown by the arrow. DERA and KLBC are 
the two portals at the ends of the structure, braced so as to resist 
the lateral wind pressures. It will be observed that the systems 
of bracing between the chords make an ordinary truss, but in a 
horizontal plane, except in the case of inclined chords like that 
of Fig. 24. In the latter case the lateral trusses are obviously 
not in horizontal planes, but they may be considered in computa- 
tions precisely as if they were. These lateral trusses are then 
treated with their horizontal panel wind loads just as the vertical 
trusses are treated for their corresponding vertical loads, and 
the resulting stresses are employed in designing web and chord 



BRIDGE PLANS AND SHOPWORK. 125 

members precisely as in vertical trusses. The wind stresses in 
the chords, in some cases, are to be added to those due to vertical 
loading, and in some cases subtracted. In other words, the 
resultant stresses are recognized and the chord members are 
so designed as properly to resist them. At the present time 
it is the tendency in the best structural work to make all the 
web members of these lateral trusses of such section that they 
can resist both tension and compression, as this contributes to 
the general stiffness of the structure. On account of the great 
variability of the wind pressures and the liability of the blows 
of greatest intensity to vary suddenly, some engineers regard 
all the wind load on structure or train as a moving load and 
make their computations accordingly. It is an excellent prac- 
tice and is probably at least as close an approximation to actual 
wind effects as the assumption of a uniform wind pressure on a 
structure. 

Both the lateral and transverse wind bracing of railroad 
bridges have other essential duties to perform than the resistance 
of lateral wind pressures. Rapidly moving railroad trains pro- 
duce a swaying effect on a bridge, in consequence of unavoidable 
unevenness of tracks, lack of balance of locomotive driving-wheels, 
and other similar influences. These must be resisted wholly by 
the lateral and transverse bracing, and these results constitute 
an important part of the duties of that bracing. These peculiar 
demands, in connection with the lateral stability of bridges, make 
it the more desirable that the lateral and transverse bracing 
should be as stiff as practicable. 

105. Bridge Plans and Shop work. — After the computations 
for a bridge design are completed in a civil engineer's office 
they are placed in the drawing-room, where the most detailed 
and exact plans of every piece which enters the bridge are 
made. The numerical computations connected with this part 
of bridge construction are of a laborious nature and must be 
made with absolute accuracy, otherwise it would be quite 
impossible to put the bridge together in the field. The various 
quantities of bars, plates, angles, and other shapes required 
are then ordered from the rolling-mill by means of these 
plans or drawings. On receipt of the material at the shop the 



126 BRIDGES. 

shopwork of manufacture is begun, and it involves a great variety 
of operations. The bridge-shop is filled with tools and engines 
of the heaviest description. Punches, lathes, planers, riveters, 
forges, boring and other machines of the largest dimensions 
are all brought to bear in the manufacture of the completed 
bridge. 

io6. Erection of Bridges. — When the shop operations are 
completed the bridge members are shipped to the site where 
the bridge is to be erected or put in place for final use. A timber 
staging, frequently of the heaviest timbers for large spans, called 
false works, is first erected in a temporary but very substantial 
manner. The top of this false work, or timber staging, is of 
such height that it will receive the steelwork of the bridge at 
exactly the right elevation. The bridge members are then 
brought onto the staging and each put in place and joined 
with pins and rivets. If the shopwork has not been done with 
mathematical accuracy, the bridge will not go together. On 
the accuracy of the shopwork, therefore, depends the possibility 
of properly fitting and joining the structure in its final position. 
The operations of the shop are so nicely disposed and so accu- 
rately performed that it is not an exaggeration to state that the 
serious misfit of a bridge member in American engineering prac- 
tice at the present time is practically impossible. This leads 
to rapid erection so that the steelwork of a pin-connected 
railroad bridge 500 feet long can be put in place on the timber 
staging, or false works, and made safe in less than four days, 
although such a feat would have been considered impossible 
twenty years ago. 

107. Statically Determinate Trusses. — The bridge structures 

which have been treated require but the simplest analysis, based 

^ ., ,..Hj. ..^ only on statical equations of equilibrium of 

^"^^ ^'U''^ forces acting in one plane, i.e., the plane 

'^'^ .,1V F of the truss. It is known from the science 

i~al7 \ X-^x of mechanics that the number of those 

!/ v,i \^ equations is at most but three for any 

'""hj system of forces or loads, viz., two equa- 

FiG. 27. tions of forces and one of moments. 

This may be simply illustrated by the system of forces F^, 



STATICALLY DETERMINATE TRUSSES. 137 

Fo, etc., in Fig. 27. Let eacli force be resolved into its vertical 
and horizontal components V and H. Also let l^, l^, etc. (not 
shown in the figure), be the normals or lever-arms dropped from 
any point A on the lines of action of the forces F^, F^, etc., so 
that the moments of the forces about that point will be F^l^, 
F^K, etc. The conditions of purely statical equilibrium are 
expressed by the three general equations 

H^-\-H^-\-etc.=F^QOs a^ + F^co^ a^-\-elc.=o\ . (35) 
T/^+ F2 + etc. =Fi sin aj + F2 sin Cg + etc. =0; . . (36) 
Ft = F J^ + FM + etc. =0 (37) 

If all the forces except three are known, obviously those three 
can be found by the three preceding equations ; but if more than 
three are unknown, those three equations are not sufficient to 
find them. Other equations must be available or the unknown 
forces cannot be found. In. modem methods of stress deter- 
minations those other needed equations express known elastic 
relations or values, such as deflections or the work performed 
in stressing the different members of structures under loads. 
A few fundamental equations of these methods will be given. 

In Figs. 19, 20, and 21 let the truss be cut or divided by the 
imaginary sections QS. Each section cuts but three members, 
and as the loads and reactions are known, the stresses in the cut 
members will yield but three unknown forces, which may be found 
by the three equations of equilibrium (35), (36), (37). If more 
than three members are cut, however, as in the section TV of 
Figs. 22 and 23, making more than three unknown equations 
to be found, other equations than the three of statical equilib- 
rium must be available. Hence the general principle that if 
it is possible to cut not more than three members by a section through 
the truss, it is statically determinate, but if it is not possible to cut 
less than four or more, the stresses are statically indeterminate. 

At each joint in the truss the stresses in the members meeting 
there constitute, with the external forces or loads acting at the 
same point, a system in equilibrium represented by the two equa- 
tions (35) and (36). If there are m such joints in the entire 
structure, there will he 2m such equations by which the same 
number of unknown quantities may be found. Since equilibrium 



138 BRIDGES. 

exists at every joint in the truss, the entire truss will be in equilib- 
rium, and that is equivalent to the equilibrium of all the external 
forces acting on it. This latter condition is expressed by the 
three equations (35), (36), and (37), and they are essentially 
included in the number 27n. Hence there will remain but 2^ — 3 
equations available for the determination of unknown stresses 
or external forces. 

If, therefore, all the external forces (loads and reactions) 
are known, the 2W — 3 equations of static equilibrium can be 
applied to the determination of stresses in the bars of the truss 
or other structure. It follows, therefore, that the greatest num- 
ber of bars that a statically determinate truss can have is 

n = 2m—T, (38) 

In Fig. 19 there are twelve joints and twenty-one members, 
omitting counter web members and the verticals ab and //, which 
are, statically speaking, either superfluous or not really bars of 
the truss. Hence 

m = i2 and 2m — 3=21 (39) 

Again, in Fig. 2 1 there are fifteen joints. Hence 
w = i5, 2 w — 3 = 27, 

and there are twenty-seven bars or members of the truss. The 
number of joints and bars in actual, statically determinate trusses, 
therefore, confirm the results. 

108. Continuous Beams and Trusses — Theorem of Three Mo- 
ments. — These considerations find direct application to what 
are known as " continuous beams," i.e., beams (or trusses) which 
reach continuously over two or more spans, as shown in Fig. 28. 

w w 

z-4 M. C-^-^ ^^ 



"7=577: 



■www; 



^|--ir-i-^--«r-#^--Z3--P 
Fig. 28. 



The beam shown is continuous over three spans, but a beam 
or truss may be continuous over any number of spans. In gen- 
eral the ends of the beam or girder may be fixed or held at the 
ends A and D, so that bending moments M and M^ at the 



CONTINUOUS BEAMS AND TRUSSES. 15^9 

same points may have value. The bending moments at the 
other points of support are represented by M^, M^, etc. The 
points of support may or may not be at the same elevation, but 
they are usually assumed to be so in engineering practice. Finally, 
it is ordinarily assumed that the continuous structure is straight 
before being loaded, and that in that condition it simply touches 
the points of support. Whether the preceding assumptions are 
made or not, a perfectly general equation can be written express- 
ing the relation between the bending moments over each set 
of three consecutive points of support, as M, M^, and M^, or M^, 
M^, and M^. Such an equation expresses what is called the 
"Theorem of Three Moments." It is not necessary to give the 
most general form of this theorem, as that which is ordinarily 
used embodies the simplifying assumptions already described. 
This simplified form of the "Theorem of Three Moments" 
applied to the case of Fig. 28 will yield the following two equa- 
tions : 



All, + 2M,(l, + 1,) + MJ, + j2W(l,'- z')z 



-^liW{l,'-z^)z^o. (40) 
^2 

+ y^W(l,'-Z')Z = 0. (41) 

The figure over the sign of summation shows the span to 
which the summation belongs. If there is but one weight or 
load W in each span, the sign of summation is to be omitted. 
In an ordinary bridge structure or beam the ends are simply 
supported and M ^M^^o. In any case if the number of sup- 
ports be n, there will hen— 2 equations like the preceding. 

If the end moments M and M^ are not zero, they will be deter- 
minable by the local conditions in each instance. In any event, 
therefore, they will be known, and there will be but n—2 unknown 
moments to be found by the same number of equations. When 
the moments are known the reactions follow from simple formulas. 



130 BRIDGES. 

109. Application to Draw- or Swing-bridges. — In general the 
reactions or supporting forces of the beams and trusses of ordi- 
nary civil-engineering practice are vertical, and all their points 
of application are known. Hence there are but two equations 
of equilibrium, equations (36) and (37), for external forces. 
These two equations for the external forces and the n — 2 equa- 
tions derived from the theorem of three moments are therefore 
always sufficient to determine the n reactions. After the reac- 
tions are known all the stresses in the bars or members of the 
trusses can at once be found. The preceding equations and 
methods as described are constantly employed in the design and 
construction of swing- or draw-bridges. 

no. Special Method for Deflection of Trusses. — The method 
of finding the elastic deflections produced by the bending of solid 
beams has already been shown, but it is frequently necessary 
to determine the elastic deflections of bridge -trusses or other 
jointed or so-called articulate frames or structures. It is not 
practicable to use the same formulae for the latter class of struc- 
tures as for the former. The elastic deflection of a bridge- or 
roof-truss depends upon the stretching or compressions of its 
various members in consequence of the tensile or compressive 
forces to which they are subjected. Any method by which the 
deflection is found, therefore, must involve these elastic changes 
of length. There are a number of methods which give the desired 
expressions, but probably the simplest as well as the most ele- 
gant procedure is that which reaches the desired expression 
through the consideration of the work performed in the truss 
members in producing their elastic lengthenings and shortenings. 

The general features of this method can readily be shown by 
reference to Fig. 29. It may be supposed that it is desired to 
find the deflection of any point, as /, of the lower chord pro- 
duced both by the dead and live load which it carries. It is 
known from what has preceded that every member of the upper 
chord will be shortened and that every member of the lower 
chord will be lengthened; and also that generally the vertical 
web members will be shortened and the inclined web members 
lengthened. If there can be obtained an expression giving that 
part of the deflection of / which is due to the change of length 



SPECIAL METHOD FOR DEFLECTION OF TRUSSES. 



131 



of any one member of the truss independently of the others, then 
that expression may be appHed to every other member in the 
entire truss, and by taking the sum of all those effects the desired 
deflection will at once result. While this expression will be found 
for some one particular truss member, it will be of such a general 
form that it may be used for any truss member whatever; it 
will be written for the upper-chord member BC in Fig, 29. 



Uo D U:i E ^ 




8 panels @ 30'=240' c. to c. end pins 

Fig. 29. 

The general problem is to determine the deflection of the point 
/when the bridge carries both dead and moving load over the 
entire span, as shown in Fig. 29. The general plan of procedure 
is first to find the stresses due to this combined load in every 
member of the truss, so that the corresponding lengthening or 
shortening is at once shown. The effect of this lengthening and 
shortening for any single member BC in producing deflection at / 
is then determined ; the sum of all such effects for every member 
of the truss is next taken, and that sum is the deflection sought. 
In this case the vertical deflection will be found, because that is 
the deflection generally desired in connection with bridge struc- 
tures, but precisely the same method and essentially the same 
formulce are used to find the deflection in any direction what- 
ever. The following notation will be employed : 

Let w = deflection in inches at any panel-point or joint of the 
truss; 

* * P = any arbitrary load or weight supposed to be hung at 

the point where the deflection is desired and act- 
ing as if gradually applied. This maybe taken as 
unity ; 

• * Z = stress produced in any member of truss by P ; 

** 5* = stress produced in any member of truss by the com- 
bined dead and moving loads ; 



132 BRIDGES. 

Let / = length in inches of any member of the truss in which 
Z or 5 is found ; 
' ' A =area of cross-section of same member in square inches ; 
" E = coefficient of elasticity. 

5 or Z may be either tension or compression, and the formulae 
will be so expressed that tension will be made positive and com- 
pression negative. 

The change of length of the chord member BC produced by a 

5 
stress gradually increasing from zero to 5 is — /. If it be sup- 
posed that BC is a spring of such stiffness that it will be com- 
pressed by the gradual application of Z exactly as much as the 
shortening of the actual member by the stress 5, the deflection 
of the point 4 with the weight P hung from it, and due to that 
compression alone, will be precisely the same as that due to the 
actual shortening of BC by the combined dead and moving loads. 

It is known by one of the elementary principles of mechanics 
that, since P acts along the direction of the vertical deflection w, 
the work performed by the weight P over that deflection is equal 
to the work performed by Z over the change of length /. Hence 

-Pw = -Z~, ^, or 
2 2 AE 

Z SI 

""^Tae ^42) 

The quantity Z -^ P is the stress produced in the member by 
a unit load applied at the joint or point where the deflection is 
desired. Again, 5-^yl is the stress per unit of area, i.e., intensity 
of stress, in the member considered by the actual dead and mov- 
ing loads. For brevity let these be written 

Z 5 

~=z and —=5; 



then 

E 



zsl 

^=^- ' ' ' (43) 



DEFLECTION METHOD APPLIED TO TRLiNGULAR FRAME. 133 



If the influence of every member of the truss is similarly ex- 
pressed, the value of the total deflection produced by the dead 
and moving loads will be 

'^-1e 



W 



(44) 



The sign of summation 2 indicates that the summation is to 
extend over all the web and chord members of the truss. 

III. Application of Method for Deflection to Triangular Frame. 

— Before applying those equations to the case of Fig. 29 it is 
best to consider a simpler case, i.e., that of the triangular frame 
shown in Fig. 18. The reactions are 



R=^jW and R' =^jW. 
The stresses in the various members are : 



(45) 



InCB, 5 = 

" CA, S = 



AB, S = 



}W sec a. 



W sec /?. 



/. 



W tan ^ = - W tan a. 



Also : CB =h sec a ; area of section =A^. 
CA = h sec /? ; " " " =^2- 
AB = l: " " " =A,. 



In this instance it is simplest to take P = W. Equation (44) 
then gives 

n.'hsec'a , h' h sec' jS , l^' I tan' l^ \W , 



w = 



P A, 



+ 



P A. 



+ 



A. 



)e 



Let it be supposed that 

/ = 2 5 feet = 300 inches ; 

/? = 8 feet 4 inches = 100 inches ; 

/j = 16 feet 8 inches = 200 inches and /^ = 100 inches ; 
tan/? = i; sec/? = 1.414; 
sec a = 2.24; 

W = 10,000 pounds. 



134 BRIDGES. 

If the bars are all supposed to be of yellow-pine timber, there 
may be taken 

£ = 1 ,000,000 pounds ; 
Aj = 10" X 1 2" = 1 20 square inches ; 
A^ = 10" X 10" = 100 square inches; 
^g = io"x 12" = 120 square inches. 

The insertion of these quantities in equation (46) gives the de- 
flection 

■z£; = . 01042 + .01253 + .oiiii =0". 034. • • • (47) 

Equation (47) is so written as to show the portion of the deflec- 
tion due to each member of the frame. 

In applying either equation (43) or equation (44) care must 
be taken to give each stress and its corresponding strain (length- 
ening or shortening) the proper sign. As the formulae have been 
written and used, a tensile stress and its resulting stretch must 
each be written positive, while a compressive stress must be 
written negative. This holds true for both the stresses Z and 5 
(or z and s). The magnitude of the assumed load P is a matter 
of indifference, since the stress Z will always be proportional to 
it and the ratio P ^Z will therefore be constant. P is frequently 
taken as unity; or, as in the case just given, it may have any 
value that the conditions of the problem make most convenient. 

112. Application of Method for Deflection to Truss. — In mak- 
ing application of the deflection formulae to any steel railroad 
truss similar to that shown in Fig. 29, it will first be necessary 
to determine the stresses in all its members due to the dead and 
moving loads, since the deflection under the moving load is 
sought. These loads will be considered uniform, and that is 
sufficiently accurate for any railroad bridge. The moving train- 
load will be taken as covering the entire span, assumed, for a 
single-track railroad, 240 feet in length between centres of end 
pins. There are eight panels of 30 feet each, and the depth of 
truss at centre is 40 feet. Other truss dimensions are as shown 
in Fig. 29. The dead loads, or own weight, are taken at 400 
pounds per linear foot of span for the rails and other pieces 
that constitute the track; at 400 pounds per linear foot for the 



APPLICATION OF METHOD FOR DEFLECTION TO TRUSS. 135 

steel floor-beams and stringers, and 1600 pounds per linear foot 
for the weight of trusses and bracing. The moving train-load 
will be taken at 4000 pounds per linear foot. This will make the 
panel-loads for each truss as follows : 

Lower-chord dead load, 30 X 800 = 24,000 pounds per panel. 
Lower-chord moving load, 30X2000 = 60,000 " " " 

Totalload on lower chord =84,000 " " " 

Upper-chord dead load, 30X400 = 12,000 " " " 

The structure is a "through" bridge, hence all moving loads 
rest on the lower chord. 




Fig. 30. 

The stresses in the truss members due to the combined uni- 
form dead and moving load are best found by the graphical 
method. One diagram only is needed to determine all the 
stresses, and it is shown in Fig. 30. This diagram is drawn 
accurately to scale, and the stresses measured from it are shown 
in the table on page 136. 

The stresses in all the truss members due to the unit load 
hung at / are readily found by the single diagram shown in 
Fig. 31, also carefully drawn to scale. These stresses measured 
from the diagram are given in the table as indicated by the column 
z ; they are also represented in equation (44) by the letter z. The 
quantity .? in equation (44) is the intensity of the stress (pounds 
per square inch of cross-section of member) produced by the 
combined dead and moving loads in each member. As shown, 



136 



BRIDGES. 



Zj 


s 


J- 


z 


/ 


TU 


+ 373,300 


+ 12,000 


+ •555 


360 


+ .08563 


^2 


+ 373,300 


+ 12,000 


+ .555 


360 


+.08563 


/^8 


4-480,000 


+ 12,000 


+ .833 


360 


+ . 1284 


^i 


+ 540,000 


+ 12,000 


+ 1.125 


360 


+•1736 


^1 


— 502,300 


— 9,000 


-.748 


472 


+.II32 


^1 


— 501,000 


-9.500 


-.870 


376 


+ .1108 


^2 


— 544,800 


— 10,000 


-I.I35 


3f>3 


+ . 1472 


^3 


— 576,000 


— 10,000 


-1.50 


360 


+ 1928 


t; 


+ 84,000 
+ 143,500 


+ 9,000 
+ 10,000 





324 
472 




^2 


+ .3738 


+ . 0629 


^2 


— 12,000 


— 1,000 


-.250 


432 


+ .00386 


5^3 


+ 93,720 


+ 7,400 


+ .456 


562 


+.0677 


^3 


+ 12,000 


+ 1,000 


-■35 


480 


— .0060 


P, 


+ 60,000 


+ 4, 800 


+ .625 


600 


+•0643 


P. 


— 12, 000 


— 1,000 





480 




1 



Deflection for \ truss members = 1.2300 inches. 
Deflection at_/=2X 1.2300 = 2.4600 inches. 




Fig. 31. 

these stresses are least in the web members near the centre of the 
span, and greatest in the chord members. The lengths in inches 
of the truss members are shown in the proper column of the table. 
It will be observed that all counter web members are omitted, 
as they are not needed for the uniform load. The coefficient of 
elasticity iE) is taken at 28,000,000 pounds. The quantities 
represented by the second member of equation (44) are com- 
puted from these data, and they appear in the last column of the 
table, the sum of which gives the desired deflection in inches. 
The elements of the table show how much of the deflection is due 
to the chords and to the web members, and they show that dis- 
regarding the latter would lead to a considerable error. 

As the deflection is usually desired in inches, the lengths of 
members must be taken in the same unit. 



METHOD OF LEAST WORK. 137 

113. Method of Least Work. — The so-called theorem or prin- 
ciple of ' ' Least Work" is closely related to the subject of elastic 
deflections just considered in its availability for furnishing equa- 
tions of condition in addition to those of a purely statical char- 
acter in cases where indetermination would result without them. 
This principle of least work is expressed in the simple state- 
ment that when any structure supports external loading the 
work performed in producing elastic deformation of all the mem- 
bers will be the least possible. Although this principle may not 
be susceptible of a complete and general demonstration, it may 
be shown to hold true in many cases if not all. The hypothesis 
is most reasonable and furnishes elegant solutions in many useful 
problems. 

The application of this principle requires the determination 
of expressions for the work performed in the elastic lengthening 
and shortening of pieces subjected either to tension or compres- 
sion, and for the work performed in the elastic bending of beams 
carrying loads at right angles to their axes. Both of these ex- 
pressions can be very simply found. 

Let it be supposed that a piece of material whose length is L 

and the area of whose cross-section is A is either stretched or 

compressed by the weight or load 5 applied §0 as to increase 

gradually from zero to its full value. The elastic change of 

SL 
length will be , E being the coefficient of elasticity. The 

average force acting will be ^5, hence the work performed in 
producing the strain will be 

-^ (48) 

2 AE 

It will generally be best, although not necessary, to take L 
in inches. The expression (48) appHes either to tension or com- 
pression precisely as it stands. 

To obtain the expression for the work performed by the 
stresses in a beam bent by loads acting at right angles to its axis, 
a differential length {dL) of the beam is considered at any normal 
section in which the bending moment is M, the total length being 
L. Let / be the moment of inertia of the normal section. A, 



138 BRIDGES. 

about an axis passing through the centre of gravity of the latter, 

and let k be the intensity of stress (usually the stress per square 

inch) at any poiat distant d from the axis about which / is taken. 

The elastic change produced in the indefinitely short length dL 

k 
when the iatensity k exists is -p.dL, If dA is an indefinitely 

small portion of the normal section, the average force or stress, 
either of tension or compression, acting through the small elastic 
change of length just given, can be written b,y the aid of equa- 
tion (5) as 

Lk.dA=^-f.dA (49) 

2 21 

Hence the work performed in any normal section of the member, 
for which M remains unchanged, will be, since J k.dA .d=M, 

^ kd.dA.dL = ^dL (50) 



/ 



>IE ■ ■ 2EI 

The work performed throughout the entire piece will then be 



/ 






Each of the expressions (48) and (51) belongs to a single piece 
or member of the structure. The total work performed in all 
the pieces subjected either to direct stress or to bending, and 
which, according to the principle of least work, must be a mini- 
mum, is found by taking the summation of the two preceding 
expressions : 

In making an application of equation (52) it is to be remembered 
that 5 is the direct stress of tension or compression in any mem- 
ber, and that M is the general value of the bending moment in 
any bent member expressed in terms of the length L. 

114. Application of Method of Least Work to General Problem, 
— ^The problem which generally presents itself in the use of equa- 
tion (52) is the finding of an equation which expresses the condi- 



METHOD OF LEAST WORK APPLIED TO TRUSSED BEAM. 139 

tion that the work expended in producing elastic deformation 
shall be a minimum, some particular stress in the structure or 
some external load or force being the variable. If t represent 
that variable, then the desired equation of condition will be found 
simply by placing the first differential coefficient of ^ in equation 
(52) equal to zero: 

de I / Y^5 dS,. , r^ rM dM,j\ , . 

dt = E{ZAdt'''^'-AjT^'^^)=''- ■ ^53^ 

The solution of equation (53) will give a value of t which will 
make the work performed as expressed inequation (52) a mini- 
mum. This method is not a difficult one to employ in such cases 
as those of drawbridges and stiffened suspension bridges. In 
the latter case particularly it is of great practical value. 

115. Application of Method of Least Work to Trussed Beam. 
— The method of least work may be illustrated by the applica- 
tion of the preceding equations to the simple truss shown in 
Fig. 32. The pieces BC and GD are supposed to be of yellow-pine 
timber, the former 10 inches by 14 inches (vertical) in section 
and the latter 8 inches by 10 inches, while each of the pieces 
BD and DC are two if -inch round steel bars. The coefficient 
of elasticity E will be taken at 1,000,000 pounds for the timber 
and 28,000,000 for the steel. The length of BC is 360 inches; 
GD 96 inches; jBZ^ =96X2.13 = 204.5 inches. 

tan a = 1.875 ^i^d sec = 2.13. 

The weight W resting at G is 20,000 pounds. A part of this 
weight is carried by BC as a simple timber beam, while the re- 
mainder of the load will be carried on the triangular frame BCD 
acting as a truss, the elastic deflection of the latter throwing a 
part of the load on BC acting as a beam. According to the 
principle of least work the division of the load will be such as 
to make the work performed in straining the different members 
of the system a minimum. 

That part of W which rests on BC as a simple beam may be 
represented by W^, while W^ represents the remaining portion 
carried by the triangular frame. As G is at the centre of the 
span, the beam reaction at either 5 or C is ^W^. Hence the 



140 



BRIDGES. 



general value of the bending moment in either half of the beam 
at any distance x from either i? or C is 

M = W^x. Hence MHL = \W,^x'dx. 

As there is but one member acting as a beam, whose moment 
of inertia / \? constant, the second term of the second member of 
equation (52) becomes, by the aid of the preceding equation, 

4-^ fMHL = ^. r\w,'x'dx = -^^^. . 
2EI J EIJq EI 96 



mmm 



(54) 




Fig. 32. 

The numerical elements of the expression for the work done 
in the members of the triangular frame are : 

Stress. 



Member. 

BC 
DC 
DG 



\W^ tan a 
^W sec a 



W. 



Length. 

360 inches = Z 

204.5 

96 " 



Area of Section. 

140 square inches 
4.14 " 
80 " " 



^_ ioXi4^ _27440 



— = 2286.7. 



The substitution of those quantities in the first term of the 
second member of equation (52) will give 



2eZj a 



W.Han^ 0.360 T7,^96 
2,000,000 \ 4X140 80 

W^ sec^ a. 204.5 _ 



+ ^ ^-^ = -000,003,7314/, . 

56,000,000 4X4.14 

The substitution of numerical quantities in equation (54) gives 



--^^ = .000,213!^,' 



Or, since W- 1^2 = "^^1' 



^ = .000, 003, 73X^2^+. 000, 213(14^ — Wj)^- 



(55) 



REMOVAL OF INDETERMINATION. 141 

Hence 

de 

= . 000,00'], 46W^ — .000, i^26{W — W^ =o. . . (56) 



dW 



2 
The solution of this equation gives 

W^ = .89314^ = 19,660 pounds. 
W,^ 340 " 

It is interesting to observe that the first term of the second 
member of equation (56) is the deflection of the point of applica- 
tion of W^ as a point in the frame, while the second term is the 
deflection of the point of application of W^ considered as a point 
of the beam. In other words, the condition resulting from the 
application of the principle of least work is equivalent to mak- 
ing the elastic deflections by W^ and 11^2 equal. Indeed equation 
(53) expresses the equivalence of deflections whenever the fea- 
tures of the problem are such as to involve concurrent deflections 
of two different parts of the structure. 

116. Removal of Indetermination by Methods of Least Work 
and Deflection. — The indetermination existing in connection 
with the computations for such trusses as those shown in Fig. 22 
and Fig. 23 can be removed by finding equations of condition 
by the aid of the method of least work or of deflections. It is 
evident that the component systems of bracing of which such 
trusses are composed must all deflect equally. Hence expres- 
sions may be found for the deflections of those component trusses, 
each under its own load. Since these deflections must be equal, 
equations of condition at once result. A sufficient number of 
such equations, taken with those required by statical equilib- 
rium, can be found to solve completely the problem. Such 
methods, however, are laborious, and the ordinary assumption 
of each system carrying wholly the loads resting at its panel- 
points is sufficiently near for all ordinary purposes. 

The method of least work can be very conveniently used for 
the solution of a great number of simple problems, like that which 
requires the determination of the four reactions under the four 
legs of a table, carrying a single weight or a number of weights, 
and many others of the same character. 



CHAPTER X. 

117. The Arched Rib, of both Steel and Masonry. — ^During 
the past ten or fifteen years the type of bridge structure called 
the arched rib has come into much use, and its merits insure for 
it a wider application in the future. It partakes somewhat of 
the nature of both truss and arch; or it may be considered a 
curved beam or girder. The ordinary beam or truss when placed 
in a horizontal position and loaded vertically yields only vertical 
reactions. Under the same conditions, however, the arched rib 
will produce both vertical and horizontal reactions, and the latter 
must either be resisted by abutments of sufficient mass, or by 
a tie-rod, usually horizontal, connecting the springing points of 
the rib. 

The arched rib may be built solid, as was done in the early 
days of bridge-building in this country when engineers like 
Palmer, Burr, and Wemwag introduced timber arches in com- 
bination with their wooden trusses, or as a curved plate girder, 
one of the most prominent examples of which is the Washington 
Bridge across the Harlem River in the city of New York; or, 
again, as a braced frame or curved truss, like the 800 feet arched 
rib carrying the roadway traffic and trolley cars across the 
Niagara gorge, or like those used in such great railroad train- 
sheds as the Grand Central Station, New York, the Pennsylvania 
stations at Jersey City and Philadelphia, and the Philadelphia 
and Reading station in Philadelphia. Those are all admirable 
examples of steel arched ribs, and they are built to sustain not 
only vertical loads but, in the case of station roofs, the normal 
or horizontal wind pressures. 

Within a few years, less than ten, another type of arched 
rib has been brought into use and promises to be one of the most 

142 



THE ARCHED RIB, OF BOTH STEEL AND MASONRY. 143 

beautiful as well as the most substantial applications of this type 
of structure; that is, the arched rib of combined steel and con- 
crete. Many examples of this type of structure already exist 
both in this country and in Europe, probably the most promi- 
nent of which in this country is that at Topeka, Kansas, across 
the Kansas River. 




Fig. 35. 

The characteristic feature of this type of structure, so far as the 
stresses developed in it are concerned, is the thrust throughout 
its length, more or less nearly parallel to its axis, which is com- 
bined with the bending moments and shears similar to those 
found in ordinary bridge -trusses. This thrust is the arch char- 
acteristic and differentiates it in a measure from the ordinary 
bridge-truss, while the bending moments and shears to which 
it is subjected differentiate it, on the other hand, from the pure 
arch type or a series of blocks in which thrust only exists. The 



144 BRIDGES. 

thrust, bending moments, and shears in arched ribs are all 
affected by certain principal features of design. Those features 
are either fixedness of the ends of the ribs or the presence of pin- 
joints at those ends or at the crown. Fig. 33 represents an 
arched rib with its ends D and F supposed to be rigidly fixed in 
masonry or by other effective means. 

118. Arched Rib with Ends Fixed. — The railroad steel arched 
bridge at St. Louis, built by Captain Eads between 1868 and 
1874, is a structure of this character. The three spans (two 
each 537 feet 3 inches and one 552 feet 6 inches in length from 
centre to centre of piers) consist of ribs the main members of 
which are composed of chrome steel. It was a structure of un- 
precedented span when it was built, and constituted one of the 
boldest pieces of engineering in its day. The chords of the ribs 
are tubes made of steel staves, and their ends are rigidly anchored 
to the masonry piers on which they rest. It is exceedingly 
difficult, indeed impossible, to fix rigidly the ends of such a 
structure, and observations in this particular instance have 
shown that the extremities of the ribs are not truly fixed, for the 
piers themselves yield a little, giving elastic motion under some 
conditions of loading. 

119. Arched Rib with Ends Jointed. — The rib shown in Fig. 
34 is different from the preceding in that pin-joints are supplied 
at each end, so that the rib may experience elastic distortion or 
strain by small rotations about the pins at A and B. In the 
computations for such a design it is assumed that the ends of the 
rib may freely change their inclination at those points. As a 
matter of fact the friction is so great, even if no corrosion exists, 
as to prevent motion, but the presence of the pins makes no bend- 
ing moment possible at the end joints, and the failure to move 
freely probably produces no serious effect upon the stresses in 
the ribs. The presence of these pin-joints simplifies the com- 
putations of stresses and renders them better defined, so that 
there is less doubt as to the actual condition of stress under a 
given load than in the type shown in Fig. 33 with ends fixed 
more or less stiffly. In Fig. 34, if the horizontal force H exerted 
by the ends of the rib against the points of support is known, 
the remaining stresses in the structure can readily be computed ; 



ARCHED Rlli WITH CROWN AND ENDS JOINTED. 145 

but neither in Fig. 34 nor in Fig. t,;^ are statical equations suffi- 
cient for the determination of stresses. Equations of condition, 
depending upon the elastic properties of the material, are re- 
quired before solutions of the problems arising can be made. 

120. Arched Rib with Crown and Ends Jointed. — The rib 
shown in Fig. 35 possesses one characteristic radically different 
from any found in the ribs of Figs. t,3 and 34, in that it is three- 
jointed, one pin-joint being at the crown and one at each end. 
So far as the conditions of stress are concerned, this is the sim- 
plest rib of all. Since there is a pin -joint at the crown as well 
as at the ends, the bending moments must be zero at each of those 
three points whatever may be the condition of loading. The 
point of application of the force or thrust at the crown, therefore, 
is always known, as well as the points of application at the ends 
of the joints. As will presently be seen, this condition makes 
equations of statical equilibrium sufficient for the determination 
of all stresses in the rib, and no equations depending upon the 
elastic properties of the material are required. The stresses in 
this class of ribs, therefore, are more easily determined than in 
the other two, and they are better defined. These qualities 
have insured for it a somewhat more popular position than 
either of the other two classes. The ribs of the great train-sheds 
of the Pennsylvania and Reading railroads in Jersey City and 
in Philadelphia belong to this class, while those of the Grand 
Central Station at New York City belong to the class shown in 
Fig. 34, as does the arched rib across the Niagara gorge, to which 
reference has already been made. 

121. Relative Stiffness of Arch Ribs. — Obviously the three- 
hinged ribs are less stiff than the two-hinged ribs or those with 
fixed ends. This is a matter of less consequence for station 
roofs than for structures carrying railroad loads. The joints of 
the two-hinged rib being at the ends of the structure, there is 
but little difference in stiffness between that class of ribs and 
those with ends fixed. Indeed the difference is so slight, and 
the uncertainty as to the degree of fixedness of the fixed ends 
of the rib is so great, that the latter type of rib possesses no real 
advantage over that with hinged ends. 



146 BRIDGES. 

122. General Conditions of Analysis of Arched Ribs. — In each 
of the three types of arched ribs shown in Figs. 33, 34, and 35 
it is supposed that all external forces act in the vertical planes 
which contain the centre lines of the various members of the rib. 
There are, therefore, the three conditions of statical equilibrium 
expressed by the three equations (35), (36), and (37). In prac- 
tically all cases, except those of arched ribs employed in roof 
construction, all the external loads are vertical. In such cases 
the equations of statical equilibrium of the entire structure may 
be reduced to two only, viz., equations (36) and (37). These 
features of the problems connected with the design of arched 
ribs will always make necessary, except in the case of the three- 
hinged rib (Fig. 35), equations of condition depending upon the 
elastic properties of the structure. 

The rib represented by Fig. 33 is supposed to have its ends 
so fixed that the inclinations of the centre line at F and D will 
never change whatever may be the loading or the variation of 
temperature. This requires the application at each of those 
points of a couple whose moment varies in value, but which is 
always equal and opposite to the bending moment at the same 
point produced by the loads imposed on the rib. It is also to 
be observed that the loads resting upon the rib are not divided 
between the points of support F and D in accordance with the 
law of the lever, since the conditions of fixedness at the ends are 
equivalent to continuity. There are then to be found, as acting 
external to the rib, the two vertical reactions and the two mo- 
ments at F and D, as well as the horizontal thrust exerted at 
the ends of the structure, which is sometimes resisted by 
the tie-rod, making five unknown quantities. Inasmuch as all 
external loading is supposed to be vertical, equations (36) and 
(37) are the only statical equations available, and three others, 
depending upon the elastic properties of the structure, must be 
supplied in order to obtain the total of five equations of con- 
dition to determine the five unknown quantities. Inasmuch 
as the end inclinations remain unchanged, the total extension 
or compression of the material at any given constant distance 
from the axis of the rib taken between the two end sections F 
and D must be equal to zero. Similarly, whatever may be the 



GENERAL CONDITIONS OF ANALYSIS OF ARCHED RIBS. 147 

amount or condition of loading, the vertical and horizontal de- 
flections of either of the ends F or D in relation to the other 
must be zero, since no relative motion between these two points 
can take place. It is not necessary in these lectures to give the 
demonstration of the equations which express the three pre- 
ceding elastic conditions, but if M is the general value of the 
bending moment for any point of the rib, and if x and y are the 
horizontal and vertical coordinates of the centre line of the rib, 
taking the central point of the section at either F or D as an 
origin, those equations, taken in the order in which the elastic 
conditions have been named, will be the following, in which n 
represents a short length of rib within which the bending moment 
ill is supposed to remain unchanged. 

) nM = o; ) nMx = o; ) nMy=o. . (57) 

D D D 

The second and third of these equations express the condition 
that the vertical and horizontal deflections respectively of the 
two ends in reference to each other shall be zero. The condi- 
tions expressed by equation (57) are constantly used in engi- 
neering practice to determine the bending moments and stresses 
which exist in the arched rib with fixed ends. The graphical 
method is ordinarily used for that purpose, as its employment 
is a comparatively simple procedure for a rib whose curvature is 
any whatever. 

If the rib has hinged joints at the ends, as in Fig. 34, obviously 
there can be no bending moment at either of those two points, 
and hence the two equations of condition which were required 
in connection with Fig. 33 to determine them will not be needed. 
There is, therefore, no restriction as to the angle of inclination of 
the centre line of the rib at those two points. Again, it is obvious 
that either end A ov B may have vertical movement, i.e., deflec- 
tion in reference to the other, without affecting the condition 
of stress in any member of the rib ; but it is equally obvious that 
neither A nor B can be moved horizontally, i.e., deflected in 
reference to the other, without producing bending in the rib and 
developing stresses in the various members. The unknown 



14:8 BRIDGES. 

quantities in this case are, therefore, only the horizontal thrust 
H exerted at the two springing points A and B, and the two 
vertical reactions, making a total of three unknown quantities, 
equations for two of which will be given by equations (36) and 
(37). The other equation required is the third expression in 
equation (57), expressing the condition that the horizontal deflec- 
tion of either of the points A or B 'm respect to the other is zero, 
since the span AB is, supposed to remain unchanged. By the 
application of the graphical method to this case, as to the pre- 
ceding, the employment of equations (36), (37), and (58) will 
afford an easy and quick determination of the three unknown 
quantities, whatever may be the curvature of the rib. 



B 



nMy=o (58) 



If the reactions and horizontal thrust H are found, stresses in 
every member may readily be computed and the complete design 
made. 

If the arch is three-hinged, as in Fig. 35, the condition that 
the bending moment must be zero at the crown C under all con- 
ditions of loading gives a third statical equation independent of 
the elastic properties of the structure which, in connection with 
equations (36) and (37), give three equations of condition suffi- 
cient to determine the two vertical reactions and the horizontal 
thrust H. In this case, as has already been stated, no elastic 
equations of condition are required. 

The determination of the end reactions, bending moments, 
and horizontal thrust H, in these various cases, is all that is 
necessary in order to compute with ease and immediately the 
stresses in every member of the rib. These computations are 
obviously the final numerical work required for the complete 
design of the structure. These procedures are always followed, 
and in precisely the manner indicated, in the design of arched ribs 
by civil engineers, whether the rib be articulated, i.e., with open 
bracing, or with a solid plate web, like those of the Washington 
Bridge across the Harlem River. 



CHAPTER XL 

123. Beams of Combined Steel and Concrete.* — A reference has 
already been made to a class of beams and arches recently come 
into use and now quite widely employed, composed of steel and 
concrete, the former being completely surrounded by and im- 
bedded in the latter. These composite beams are very exten- 
sively used in the floors of fire-proof buildings as well as for other 
purposes. Arches of combined concrete and steel were probably 
first built in Germany and but a comparatively few years ago. 
During the past ten years they have been largely introduced 
into this country, and many such structures have not only been 
designed but built. The most prominent design of arches of 
combined concrete and steel are those of the proposed memorial 
bridge across the Potomac River at Washington, for which a 
first prize was awarded as the result of a national conipetition 
in the early part of 1900. So far as the bending or flexure of 
these composite beams and arches is concerned, the theory is 
identically the same for both, the formulae for each of which are 
given below. In order to express these formulas the following 
notation will be needed : 

P is the thrust along the arch determined by the methods 
explained in the consideration of arched ribs. 

/ is the distance of the line of the thrust P from the axis of 
the arched rib. 

E^ and E^ are coefficients of elasticity for the two materials. 

A^ and A^ are areas of normal section of the two materials. 

/j and /j are moments of inertia of ^4^ and A^ about the neutral 
axes of the composite beam or arch sections. 

* For a complete and detailed statement of this whole subject, including design 
work, reference should be made to the author's "Elasticity and Resistance of Materials." 

149 



150 



BRIDGES. 



■ ^¥'- 


-C 


- j'*»? / lift: 1 ,-'-■ 

\ 1 ■ 


* 




'- Ili^^Jl 




^ -5; 



O c 
^ - 



fe — 






BEAMS OF COMBINED STEEL AND CONCRETE. 



151 




153 BRIDGES. 

k^ and ^2 ^i"® intensities of bending stress in the extreme 
fibres of the two materials. 

h^ and h^ are total depths of the two materials. 

d^ and d^ are distances from the neutral axes to farthest fibres 
of the two materials; distances to other extreme fibres would 
be {h^ — d^ and {h^ — d^) . 

W^ and W^ are loads, either distributed or concentrated, car- 
ried by the two portions. 

W = W^ + W.^ is total load on the beam or arch. 

^1 = -^ and ^2 = ^; ••?i + ^2 = i; ^ = ^-- 

The application of the theory of flexure to the case of a beam 
or arch of two different materials, steel and concrete in this case, 
will give the following results : 

M = PI; hence M,=q,Pl and M^ = q,Pl. . . (59) 

^^=#=£7:w2- ^'°^ 

q=^= £2^2 (6,) 



W EJ^ + EJ 



P Md y ,. . 

+ r , .r • ' (62) 



^1,-1-^2 /i + ^/; 

P MJ 



These formulas exhibit some of the main features of the 
analysis which must be used in designing either beams or arches 
of combined steel and concrete. In the use of these equations 
care must be taken to give the proper sign to the bending moment 
M. They obviously apply to the combination of any two mate- 
rials, although at the present time the only two used in such com- 
posite structures are steel and concrete. If the subscript i 
belongs to the concrete portion, and the subscript 2 to the steel 
portion, there may be taken £j^ = 1,500,000 to 3,000,000 and 
£^2 = 30)Ooo>ooo- Hence ^ = 20 to 10. 

The purpose of introducing the steel into the concrete is to 
make available in the composite structure the high tensile resist- 



BEAMS OF COMBINED STEEL AND CONCRETE. 153 

ance of that metal. A very small steel cross-section is sufficient 
to satisfactorily accomplish that purpose. The percentage of the 
total composite section represented by the steel will vary some- 
what with the dimensions of the structure and the mode of using 
the material; it will usually range from 0.75 per cent to 1.5 per 
cent of the total section. The large mass of concrete in which 
the steel should be completely imbedded serves not only to afford 
a large portion of the compressive resistance required in both 
arches and beams, but also to preserve the steel effectively from 
corrosion. Many experiments have shown that it requires but a 
small per cent of steel section to give great tensile resistance to 
the composite mass. 



CHAPTER XII. 

124. The Masonry Arch. — The masonry arch is so old that 
its origin is lost in antiquity, but its complete theory ha.s been 
developed with that of other bridge structures only within the 
latest period. It is only possible here to give some of the main 
features of that theory and a few of the fundamental ideas on 
which it is based. It is customary among engineers to regard 
the masonry arch as an assemblage of blocks finely cut to accu- 
rate dimensions, so that the assumption of either a uniform or 
uniformly varying pressure in the surface of contact between 
any two may be at least sufficiently near the truth for all practical 
purposes. Although care is taken to make joints between ring- 
stones or voussoirs completely cemented or filled with a rich 
cement mortar, it is usually the implicit assumption that such 
joints do not resist tension. As a matter of fact many arch 
joints are capable of resisting considerable tension, but, in conse- 
quence of settlement or shrinkage, cracks in them that may be 
almost or quite imperceptible frequently prevent complete con- 
tinuity. It is, therefore, considered judicious to determine the 
stability of the ordinary masonry arch on the assumption that 
the joints do not resist tension. 

In these observations it is not intended to convey the impres- 
sion that no analysts treat the ordinary arch as a continuous 
elastic masonry mass, like the composite arches of steel and con- 
crete. Although much may be said in favor of such treatment 
for all arches, it is believed that prolonged experience with arch 
structures makes it advisable to neglect any small capacity of 
resistance to tension which an ordinary cut-stone masonry joint 
may possess, in the interests of reasonable security. 

The ring-stones or voussoirs of an arch are usually cut to form 
circular or elliptic curves, or to lines which do not differ sensibly 

154 



OLD AND NEW THEORIES OF THE ARCH. 155 

from those curves. The arch-ring may make a complete semi- 
circle, as in the old Roman arches, or a segment of a semicircle ; 
or the stones may be arranged to make a pointed arch, like the' 
Gothic ; or, again, a complete semiellipse may be formed, or pos- 
sibly a segment of that curve. When a complete semiellipse 
or complete semicircle is formed, the arches are said to be full- 
centred, and in those cases they spring from a horizontal joint 
at each end. On the other hand, segmental arches spring from 
inclined joints at each end called skew-backs. 

125. Old and New Theories of the Arch. — In the older theories 
of the arch, considered as a series of blocks simply abutting against 
each other, the resultant loading on each block was assumed to 
be vertical. In the modern theories, on the other hand, the 
resultant loading on any block is taken precisely as it is, either 
vertical or inclined, as the case may be. Many arches are loaded 
with earth over their arch-rings. This earth loading produces 
a horizontal pressure against each of the stones, as well as a 
vertical loading due to its own weight. In such cases it is neces- 
sary to recognize this horizontal or lateral pressure of the earth, 
as it is called, as a part of the arch loading. 

It is known from the theory of earth pressure that the amount 
of that pressure per square foot or any other square Unit may vary 
between rather wide limits, the upper of which is called the abut- 
ting power of earth, and the latter the conjugate pressure due to 
its own weight only. If w is the weight per cubic unit of earth 
and X the depth considered, and if (p be the angle of repose of the 
earth, the abutting power per squate unit will have the value : 

I -t- sin (p ,. s 

p=wx , — -, (04) 

I — sm f 

while the horizontal or conjugate pressure due to the weight of 
earth only will be : 

- I — sin (f f^s 

p' =wx .^ (05) 

I -fsm (p 

The use of these formulas will be illustrated by actual arch com- 
putations. 



156 



BRIDGES. 



Fig. 36 is supposed to show a set of ring-stones for an arch of 
any curvature whatever. The joints LM and ON represent 
the skew-backs or springing joints, while R and R^ represent the 
supporting forces or reactions with centres of action at a' and a^. 

Fig. 36. 




The ring is divided into blocks or pieces by the joints at a, b, c, d, 
and e, the resultant loading or force on each block being given by 
the lines with arrow-heads and numbered i, 2, 3, 4, 5, 6, and 7. 
Fig. 37 represents a force polygon constructed in the ordinary 
manner by laying off carefully to scale the two reactions R and R^, 
together with the loads or forces numbered i to 7, inclusive. 
By constructing the so-called polygonal frame in the ring-stones 
of Fig. 36 in the usual manner with its lines or sides parallel to 



OLD AND NEW THEORIES OF THE ARCH. 157 

the radiating lines in Fig. 37, as shown by the broken lines, the 
points a, b, c, etc., are found where the resultant forces cut each 
joint. The line drawn through those points thus determined 
is called the line of resistance of the arch. Obviously, if that line 
of resistance be determined, the complete stability or instability 
of the arch, as the case may be, will be established. Furthermore, 
the complete determination of the force polygon in Fig. 37, and 
the corresponding polygonal frame drawn in the arch-ring, con- 
stitute all the computations involved in the design of an arch. 

The thrust 7^ at the crown, shown both in Fig. 36 and Fig. 37, 
is frequently horizontal, although not necessarily so ; its value 
is shown by Fig. 37. In the older arch theories a principle 
was enunciated called the "principle of least resistance." The 
thrust Tg is a fundamental and so-called passive force. That is, 
its magnitude depends not only upon its position, but also largely 
upon the magnitude of the active forces which represent the 
loading on the arch-ring. Under the principle of least resistance 
it was laid down as a fundamental proposition, in making arch 
computations, that this passive force T^ must be the least possi- 
ble consistent with the stability of the structure. While this 
provisional proposition answered its purpose well enough, there 
are other clearer methods of procedure which are thoroughly 
rational and involve the employment of no extraneous consider- 
ations other than those attached to the determination of statical 
equilibrium. 

A scrutiny of the conditions existing in Fig. 36 will show that 
if the external forces or loadings on the individual blocks of the 
ring are given, four quantities are to be determined, viz., the 
two reactions R and R^ and their lines of action. Inasmuch as 
no elastic features of the structure are to be considered, there 
are available for the determination of these four quantities the 
three equations of equilibrium, equations (35), (36), and (37), 
which are not sufficient for the purpose. If one line of action, 
such as that oi R, be located by assuming its point of applica- 
tion a', the three equations just named will be sufficient for the 
determination of the remaining three equations ; and that is pre- 
cisely the method employed. It is tentative, but perfectly prac- 
ticable. If, instead of assuming one of the points of application 



158 BRIDGES. 

of the reactions, we assume both of those points and construct 
a trial polygonal frame, it will be necessary to use but two of the 
three equations of statical equilibrium. For that purpose there 
are employed equations (35) and (36), but in a graphical manner, 
which will presently be illustrated. 

126. Stress Conditions in the Arch-ring. — Before proceeding 
to the construction of an actual line of resistance, a little consid- 
eration must be given to the stress conditions in the arch-ring. 
As the joints are considered capable of resisting no tension, the 
dimensions of the arch-ring must be finally so proportioned that 
pressure only will exist in each and every joint. If each centre 
of pressure, as a, b, etc., in Fig. 36, is found in the middle third 
of the joint, it is known from a very simple demonstration in 
mechanics that no tension will ever exist in that joint, although 
the pressure may be zero at one extremity and a maximum at 
the other. This is the condition usually imposed in designing 
an arch-ring to carry given dead or live loads. It is usually 
specified that ' ' the line of resistance of the ring must lie in the 
middle third." It must be borne in mind, however, that the 
stability of the ring is perfectly consistent with the location of 
the line of resistance outside of the limits of the middle third, 
provided it is not so far outside as to induce crushing of the ring- 
stones. Whenever that crushing begins the arch is in serious 
danger and complete failure is likely to rCvSult. 

127. Applications to an Actual Arch. — These principles will 
be applied to the arch-ring shown in Fig. 38, in which the clear 
span TU is 90 feet. The radius CO of the soffit (as the under 
surface of the arch is called) is 50 feet, the ring being circular 
and segmental. The uniform thickness of the ring shown at 
the various joints is assumed at 4 feet as a trial valae. The load- 
ing above the ring to the level of the line E'O is assumed to be 
dry earth weighing, when well rammed in place, 100 pounds per 
cubic foot. The depth of this earth filling at the crown n of the 
arch is taken at 4 feet. The ring-stones are assumed to be of 
granite or best quality of limestone, weighing 160 pounds per 
cubic foot. The ' thickness or width of arch-ring of one foot is 
assumed, as each foot in width is like every other foot, and the 
loads are taken for that width of ring. The rectangle EJJ'E' 



APPLICATIONS TO AN ACTUAL ARCH. 



159 



is supposed to represent a moving load covering one half of the 
span and averaging 500 pounds per linear foot; in other words, 
averaging 500 pounds per square foot of upper surface projected 
in the line E'O. The total length of the arch-ring, measured 
on the soffit, is about 113 feet, and it is divided into ten equal 
portions for the purpose of convenient computation. The radial 
joints so located are as shown at de, fg, hk. From the points 
where these joints cut the extrados (as the upper surface of the 
arch-ring is called) vertical broken lines are erected, as shown 
in Fig. 38. 



K L M N O 




C 

Fig. 38. 
The horizontal line drawn to the left from / gives the vertical 
projection of that part of the extrados between d and /, and the 
horizontal earth pressure on df will be precisely the same in 
amount as that on the vertical projection of df, as just found. 
In the same manner the horizontal earth pressure on that part of 
the extrados between any two adjacent joints may be found. 
The mid-depths of these vertical projections below the line E'O 
are to be carefully measured by scale and then used for the values 
of X in equations (64) and (65), which now become equations 
(66) and (67), as the angle of repose (p is taken to correspond to 
a slope of earth surface of i vertical on i^ horizontal. 

^ = 3.51^:^ (66) 

p' =o.2^'^wx (67) 

The horizontal earth pressures thus found are as follows : 

7 _ ( 101,500 pounds; , _ ( 30,625 pounds; 
'~ \ 8,700 " ^'- \ 2,625 '' 

h - i 59-500 " /, _ J 9.800 

^^" ( 5,100 - ^^-\ 840 " 



160 BRIDGES. 

These quantities h^, etc., are found by multiplying the two inten- 
sities p and p' by the vertical projections of the surface on which 
they act. The larger values are found by equation (66) and 
represent the abutting power of the earth, while the smaller values 
are found by equation (67), and represent the horizontal or con- 
jugate pressure of the earth due to its own weight only. The 
actual horizontal earth pressure against the arch-ring may lie 
anywhere between these limits. 

The weights of the moving load, earth, and ring-stones between 
each pair of vertical lines and radial joints shown in Fig. 38 are 
next to be determined, and they are as follows : 

W^ = 27,300 pounds; W^=- 12,300 pounds; 

^^2 = 27,900 ' ^^7 = 15.550 

1^3 = 24,500 " 1^3 = 19,500 " 

1^4 = 21,300 " 1^9=19,400 " 

1^, = 18,300 " W^,, = 24,300 " 

The centres of gravity of these various vertical forces are shown 
in Fig. 38 at the points W.^, W^, etc. The triangles of forces shown 
in that figure and composed, each one, of a vertical and horizontal 
force as described, are laid down in actual position on the arch- 
ring, as shown. All data are thus secured for completing the 
force polygon and polygonal frame or line of resistance. It will 
be assumed that the reactions R and R' cut the springing joints 
at c and a, respectively, one third of the width of the joint from 
the soffit, and it will further be assumed that b, the mid-point of 
the joint at the crown, is also in the line of resistance. The 
assumption of the location of these three points is made for the 
reason, as is well known, that with a given system of forces a 
polygonal frame may be found which will pass through any three 
points in the ring. 

The force polygon B, i, 2, 3, . . . , 10, A, Fig. 39, is then 
drawn with the loadings on each ring segment found as already 
explained. The horizontal forces are taken as represented by 
the smaller values of h^, h^, h^, h^. Other force polygons wdth 
larger values of these horizontal forces were tried and not found 
satisfactory. Having constructed the force polygon and assumed 
the trial pole P' , the radial lines are drawn from it as shown in 



APPLICATIONS TO AN ACTUAL ARCH. 



161 



Fig. 39. The polygonal frame shown in broken lines in Fig. 38 
results from this trial pole. The frame practically passes through 
b and c, but leaves the ring, passing outside of it, above the 
joint VU. The point q in this frame is vertically above a. The 
' ' three-point " method of finding the frame that will pass through 




\ SCALE 1 =30000 LBS. 



Fig. 39. 

a, b, and c was then employed. The line ^6, Fig. 39, was drawn; 
then P'D was drawn parallel to gb, Fig. 38 (not shown) ; after 
which PD was drawn parallel to ab, until it intercepted the hori- 
zontal line PQ, the line P'Q having previously been drawn par- 
allel to qc (not shown). The final pole P was thus found. The 
polygonal frame shown in full lines in the arch-ring was then 
drawn with sides parallel to the lines radiating from P, all in 
accordance with the usual methods for such graphic analysis. 
That polygonal frame lies within the middle third of the arch- 



162 BRIDGES. 

ring, although at three points it touches the limit of the middle 
third. The arch, therefore, is stable. 

This construction shows that, with the actual loading of the 
ring, a line of resistance can be found lying within the middle 
third; its stability under the conditions assumed is, therefore, 
demonstrated. It does not follow that the line of resistance as 
determined must necessarily exist, since there may be others 
located still more favorably for stability. This indetermination 
results from the fact already observed that the equations of 
statical equilibrium are not sufficient in number to determine 
the four unknown quantities (the two horizontal and the two 
vertical reactions) ; but the process of demonstrating the stability 
of the arch-ring is simple and sufficient for all ordinary purposes. 
The line of resistance found, if not the true one, is so near to it 
that no sensible waste of material is involved in employing it. 
This indetermination has prompted some engineers and other 
analysts to consider all arch-rings as elastic, thus obtaining other 
equations of condition. While such a procedure may be per- 
missible, it is scarcely necessary, and perhaps not advisable, in 
view of the fact that many joints of cut-stone arches become 
slightly open by very small cracks, resulting possibly from un- 
equal settlement, quite harmless in themselves, having practi- 
cally no effect upon the stability of the structure. 

128. Intensities of Pressure in the Arch-ring. — It still re- 
mains to ascertain whether the actual pressures of masonry in 
the arch-ring are too high or not. The greatest single force 
shown in the force polygon in Fig. 39 is the reaction R, having 
a value by scale of 122,000 pounds, under the left end of the arch, 
and it is supposed to act at the limit of the middle third of the 
joint. Hence the average pressure on that joint will be 

122 000 yc 2 

'- =61,000 pounds per square foot. 

This value may be taken as satisfactory for granite or the best 
quality of limestone. 

Again, it is necessary in bridges, as in some other structures, 
to determine whether there is any liability of stones to slip on 
each other. In order that motion shall take place the resultant 



PERMISSIBLE WORKING PRESSURES. 163 

forces acting on the surface of a stone joint must have an incli- 
nation to that surface less than a value which is not well deter- 
mined and which depends upon the condition of the surface of 
the stone; it certainly must be less than 70°. The inclination 
of every resultant force in Fig. 38 to the surface on which it acts 
is considerably greater than that value and, hence, the stability 
of friction is certainly secured. 

129. Permissible Working Pressures. — The working values of 
pressures permissible on cut-stone and brick or other masonry 
must be inferred from the results of the actual tests of such 
classes of masonry in connection with the results of experience 
with structures in which the actual pressures existing are known. 
It is safe to state that with such classes of material as are used 
in the best grade of engineering structures these pressures will 
generally be found not to exceed the following limits : 

Concrete, 20,000 to 40,000 pounds per square foot. 

Cement rubble, same values. 

Hard-burned brick, cement-mortar joints, 30,000 to 50,000 
pounds per square foot. 

Limestone ashlar, 40,000 to 60,000 pounds per square foot. 

Granite ashlar, 50,000 to 70,000 pounds per square foot. 

The masonry arch is at the same time the most graceful and 
the most substantial and durable of all bridge structures, and it 
is deservedly coming to be more and more used in modem bridge 
practice. One of the greatest railroad corporations in the United 
States has, for a number of years, been substituting, wherever 
practicable, masonry arches for the iron and steel structures 
replaced. The high degree of excellence already developed in 
this country in the manufacture of the best grades of hydraulic 
cement at reasonable prices, and the abundance of cut stone, 
has brought this type of structure within the limits of a sound 
economy where cost but a few years ago would have excluded it. 
It is obviously limited in use to spans that are not very great 
but yet considerably longer than any hitherto constructed. 

130. Largest Arch Spans.^The longest arch span yet built 
has been but recently completed in Germany at the city of 
Luxemburg. This bridge has a span of 275.5 feet and a rise of 
1 01. 8 feet. It is rather peculiarly built in two parallel parts 



164 



BRIDGES. 




LARGEST ARCH SPANS. 



165 



separated 19.5 feet in the clear, the space between being spanned 
by slabs or beams of combined concrete and steel. The arch- 
ring is 4.75 feet thick at the crown and 7.18 feet thick at a point 
53.14 feet vertically below the crown where it joins the spandrel 
masonry. The roadway is about 52.5 feet wide and 144.5 ^eet 
above the water in the Petrusse River, which it spans. 

The longest arch in this country is known as the Cabin John 
Bridge of 220 feet span and 57.5 feet rise. It is a segmental 
arch, and is located a short distance from the city of Washington, 




Cabin John Bridge, near Washington, D. C. 

carrying the aqueduct for the water-supply of that city. These 
lengths of span may be exceeded in good ordinary masonry con- 
struction, but the high degree of strength and comparative 
lightness which characterize the combination of steel and con- 
crete will enable bridges to be built in considerably greater spans 
than any yet contemplated in cut-stone masonry. 



CHAPTER XIII. 



131. Cantilever and Stiffened Suspension Bridges. — There are 

two other types of bridges of later development which have, in 
recent years, become prominent by remarkable examples of both 
completed structure and design; they are known as the canti- 
lever and stiffened suspension bridges. Both are adapted to 
long spans, although the latter may be applied to much longer 
spans than the former. A cantilever structure, with a main 
span of 1800 feet between centres of piers, is now in process of 
construction across the St. Lawrence River at Quebec, while the 
well-known Forth Bridge across the Firth of Forth in Scotland 
has a main span of 17 10 feet. The longest stiffened suspension 
bridge yet constructed is the New York and Brooklyn Bridge, 
with a river span of about 1595.5 ^^^"t between centres of towers, 
but the stiffened suspension system has been shown by actual 
design to be applicable to spans of more than 3200 feet, with 
material now commercially produced. 

132. Cantilever Bridges. — Figs. 41 and 42 exhibit in skeleton 
outline two prominent cantilever designs for structures in this 




(<■ U Panel.-orSO — 840:- -^ijo*-— 12 PaneU or60'= 72(>i -jjj - -^''- f[?2j' 



Total Length C. to C. of End Pins = 4120 Ft. 



Fig. 41. 

country. That shown in Fig. 41 was intended for a bridge across 
the Hudson River between Sixtieth and Seventieth streets. New 
York City. The main central opening has a span of 1800 feet, 
and a length of 2000 feet between centres of towers. Fig. 42 
shows the Monongahela River cantilever bridge,* now being 

* This Ijridge was designed by and is being constructed under the direction of 
Messrs. Boiler and Hodge, Consulting Engineers, New York City. 

166 



CANTILEVER BRIDGES. 



167 



?: 



tdj:: 



built at Pittsburgh, Penn. Both fig- ^-^ — -S" 

ures exhibit the prominent features 
of the cantilever system. The main 
parts are the towers, at each end of 
the centre span, which are 534.5 feet ^ 
high in the North River Bridge and -j^ 
135 feet high in the Monongahela '| 
River structure, and the central main o 
or river span with its simple non- g 
continuous truss hung from the ends ^ 
of the cantilever brackets or arms ^ 
which flank it on both sides. These ^ 
cantilever arms are simply projecting ^ 
trusses continuous with the shore- I 
or anchor-arms. They rest -on the ^ 
piers at either end of the main span, ^ 
as a lever rests on its fulcrum. This ^ 
arrangement requires the shore ex- ^ 
tremities or the anchor-arms to be 3 
anchored down by a heavy weight ^. 
formed by the masonry piers at those 5^ 
points. Recapitulating and starting ^ 
from the two shore ends of the struc- ^ 
ture, there are the anchor-spans, con- ° 
tinuous at the towers, with the can- k. 
tilever arms projecting outward to- 3 
ward the centre of the main opening ^ 
and supporting at their ends the ^ 
suspended truss, which is a simple, ^ 
non-continuous one. It is thus evi- ^ 
dent that the cantilever bridge is a " 
structure composed of continuous 5' 
trusses with points of contraflexure c 
permanently fixed at the ends of the ^ 
suspended span. The greatest bend- 
ing moments are at the towers, and ^^ ""f.^ 
the great depth at that point is given 
for the purpose of affording adequate 



? § 



-s/f- 



168 BRIDGES. 

resistance to those moments by the members of the structure. 
The following statement shows some elements of the more 
prominent cantilever bridges of this country and of the Forth 
Bridge : 

Length of Cantilever 
Name. Opening, Centre to Total Length, 

Centre of Towers. 

Pittsburgh 812 feet. 1504 feet. 

Red Rock(Colo.) 660 " 990 " 

Memphis (Tenn.) 790.48"- 2378.2 

Forth 1710 " 5330 " 

The arrangement of web members of cantilever structures is 
designed to be such as will transfer the loads from the points of 
application to the points of support in the shortest and most 
direct paths. Both Figs. 41 and 42 show these general results 
accomplished by an advantageous arrangement of web members. 

It is interesting to note that the first cantilever bridge de- 
signed and built in this country was constructed in 1871. This 
structure was designed and erected by the late C. Shaler Smith, 
a prominent civil engineer of his day. 

133. Stiffened Suspension Bridges. — The stiffened suspension 
bridge is a structure radically different in its main features and 
its mode of transferring load to points of support from any here- 
tofore considered, except arched ribs. When a load is supported 
by a beam or truss, the stresses, either in the web members of 
the truss or in the solid web of the beams, travel up and down 
those members in zigzag directions with a relatively large amount 
of metal required for that kind of transference. That metal 
is represented by the weight of the web members of the truss and 
of the solid web of the beam. Again, there are two sets of truss 
members — the chords or flanges, one of which sustains tension 
and the other an equal amount of compression. The greater 
part of this metal must be so placed and used that the working 
intensities of stress are comparatively small. This is particu- 
larly the case in compression members of both chords and webs 
which constitute the greater portion of the weight of the truss. 
All compression members are known as long columns which sus- 
tain not only direct compression but bending, and the amount 



STIFFENED SUSPENSION BRIDGES. 169 

of stress or load which they carry per square inch is relatively 
small, decreasing as the length increases. For all these reasons 
the amount of metal required for both beams and trusses is com- 
paratively large. In suspension bridges, however, the condi- 
tions requiring the employment of a relatively large amount of 
metal with relatively small unit stresses are absent. The main 
members of a suspension bridge are the cables and the stiffening 
trusses, the latter being light in reference to the length of span. 
The cables are subjected to tension only, which is the most eco- 
nomical of all methods of using metal. A member in tension 
tends to straighten itself, so that it is never subjected to bending 
by the load which it carries. The opposite condition exists with 
compression members. Again, grades of steel possessing the 
highest ultimate resistance may be used in the manufacture of 
cables. It is well known that w;ire is the strongest form in which 
either wrought iron or steel can be manufactured. While the 
ultimate tensile resistance of ordinary structural steel will seldom 
rise above 70,000 pounds per square inch, steel wire, suitable to 
be used in suspension-bridge cables, may be depended upon, at 
the present time, to give an ultimate resistance of at least 180,000 
pounds per square inch. The elastic limit of ordinary struc- 
tural steel is but little above half its ultimate resistance, while 
the elastic limit of the steel used in suspension-bridge cables is 
probably not less than three fourths of its ultimate resistance. 
It is seen, therefore, that the high resistance of steel wire makes 
the steel cable of the suspension bridge a remarkably economical 
application of metal to structural purposes. 

The latest example of stiffened suspension -bridge is the new 
East River Bridge reaching across the East River from Broadway 
in Brooklyn to Delancey Street, New York City, now being built, 
with a main span of 1600 feet between centres of towers. The 
entire length of the metal structure is 7200 feet, and the eleva- 
tion of the centres of cable at the tops of the towers is 333 feet 
above mean high water. 

Fig. 43 shows a view of this bridge. Its three principal divi- 
sions are the cables, the stiffening trusses, and the towers. The 
latter afford suitable points of support for the cables, which not 
only extend over the river span, but are carried back to points 



170 



BRIDGES. 



on the land where they are securely attached to a neavy mass 
of anchorage masonry. These anchorages must be sufficiently 
heavy to prevent any load which may come upon the bridge 
from moving them by the pull of the cables. It is usual to 




Fig. 43. — New £-ast River Bridge. 

make these masses so great that they are capable of resisting 
fromi two to two and a half times the pull of the cables. 

134. The Stiffening Truss. — The function of the stiffening 
trusses is peculiar and imperatively essential to the proper action 
of the whole system. If they are absent and a weight should 
be placed upon the cable at any point, a deep sag at that point 
would result. If a moving load should attempt to pass along a 
roadway supported by a cable only, the latter would be greatly 
distorted, and it would be impossible to use such a structure for 
ordinary traffic. Some means must then be employed by which 
the cable shall maintain essentially the same shape and position, 
whatever may be the amount of loading. It can be readily 
shown that if any perfectly flexible suspension-bridge cable carries 
a load of uniform intensity over the span from one tower to the 
other, the curve of the cable will be a parabola, with its vertex at 
the lowest point. Furthermore, it can also be shown that if any 
portion of the span be subjected to a uniform load, the corre- 
sponding portion of the cable will also assume a parabolic 



LOCATION AND ARRANGEMENT OF STIFFENING TRUSSES. 171 

curve. It is assumed in all ordinary suspension-bridge design 
that the total weight of the structure, including the cables and 
the suspension-rods which connect the stiffening trusses to the 
cable, is uniformly distributed over the span, and that assump- 
tion is essentially correct. So far as the weight of the structure 
is concerned, therefore, the curve of the cable will always be 
parabolic. It only remains, therefore, to devise such stiffening 
trusses as will cause any moving load passing on or over the 
bridge to be carried uniformly to the cables throughout the 
entire span. This condition means that if any moving load 
whatever covers any portion of the span, the corresponding pull 
of the suspension-rods on the cables must be uniform from one 
tower to the other, and that result can be practically accom- 
plished by the proper design of stiffening trusses; it is the 
complete function of those trusses to perform just that duty. 

135. Location and Arrangement of Stiffening Trusses. — It has 
been, and is at the present time to a considerable extent, an open 
question as to the best location and arrangement of the stiffening 
trusses. The more common method in structures built is that 
illustrated by the New York and Brooklyn and the new East 
River bridges. Those stiffening trusses are uniform in depth, 
extending from one tower to the other, or into the land spans, 
and connected with the cables by suspension-rods running from 
the latter down to the lower chords of the trusses. It is obvious 
that the floor along which the m.oving load is carried must have 
considerable transverse stiffness, and hence it may appear advis- 
able to place the stiffening trusses so that the floor may be carried 
by them. On the other hand, some civil engineers maintain 
that it is a better distribution of stiffening metal to place it where 
the cables themselves may form members of the stiffening trusses, 
with a view to greater economy of material. 

Figs. 44, 45, and 46 illustrate some of the principal proposed 
methods of constructing stiffening trusses in direct connection 
with the cables. The structure shown in Fig. 44 illustrates the 
skeleton design of the Point Bridge at Pittsburgh. The curved 
member is a parabolic cable composed of eye-bars. This para- 
bolic cable carries the entire weight of the structure and 
moving load when uniformly distributed. If a single weight 



172 



BRIDGES. 



rests at the centre, the two straight members of the upper chord 
may be assumed to carry it. If a single weight rests at any 
other point of the span, it will be distributed by the bracing 
between the straight and curved members of the stiffening truss. 
Obviously the most unbalanced loading will occur when one half 
of the span is covered with moving load. In that case the bow- 
string stiffening truss in either half of Fig. 44 will make the re- 




FlG. 46. 

quired distribution and prevent the parabolic tension member 
from changing its form. 

The type of bracing shown in Fig. 45 possesses some advan- 
tages of a peculiar nature. Each curved lower chord of the 
stiffening truss corresponds to the position of the perfectly flexi- 
ble cable with the moving load covering that half of the span 
which belongs to the greatest sag of the cable. The two para- 
bolic cables thus cross each other in a symmetrical manner at 
the centre of the span. If the moving load covers the entire 
span, the line of resistance or centre line of imaginary cable will 
be the parabola, shown by the broken line midway along each 
crescent stiffening truss. The diagonal bracing placed between 
the cables is so distributed and applied as to maintain the posi- 
tions of cables under all conditions of loading. 

The mode of constructing the stiffening truss between two 



DIVISION OF LOAD. 173 

cables, shown in Fig. 46, is that adopted by Mr. G. Lindenthal 
in his design for a proposed stiffened suspension bridge across 
the Hudson River with a span of about 3000 feet. The two 
cables are parabolic in curvature and may be either concentric 
or parallel. This system of stiffening bracing possesses some 
advantages of uniformity and is well placed to secure efficient 
results. The same system has been used in suspension bridges 
of short span by Mr. Lindenthal at both St. Louis and Pittsburgh. 
The stiffening bracing produces practically a continuous stiffening 
truss from one tower to the other, whereas the systems shown 
in Figs. 44 and 45 involve practically a joint at the centre of the 
span. 

In all these three types of vertical stiffness the floor is designed 
to meet only the exigencies of local loading, being connected 
with the stiffening truss above by suspension bars or rods, prefer- 
ably of stiff section. 

When stiffening trusses are placed along the line of the floor, 
as in the case of the two East River bridges, to which reference 
has already been made, those trusses need not necessarily be 
of uniform depth, and they may be continuous from tower to 
tower or jointed at the centre, like those of the New York and 
Brooklyn suspension bridge. This centre joint detracts a little 
from the stiffness of the structure, but in a proper design this 
is not serious. 

136. Division of Load between Cables and Stiffening Truss. — 
In a case where continuous stiffening trusses are employed it is 
obvious that they may carry some portion of the moving load 
as ordinary trusses. The portion so carried will be that which 
is required to make the deflection of the stiffening truss equal to 
that of the cable added to the stretch of the suspension-rods. 
In the old theory of the stiffening truss constructed along the 
floor of the bridge this effect was ignored, and the computations 
for the stresses in those trusses were made by the aid of equations 
of statical equilibrium only. That assumption, that the cable 
carried the entire load, was necessary to remove the ambiguity 
which would otherwise exist. In modern suspension-bridge 
design those trusses may be assumed continuous from tower to 
tower with their ends anchored at the towers, or they may be 



174 BRIDGES. 

designed to be carried continuously through portions of the land 
spans and held at their extremities by struts reaching down to 
anchorages, so that those ends may never rise nor fall, but move 
horizontally if required. If there are no pin-joints in the trusses 
at the centre and ends of the main span, equations of statical 
equilibrium are not sufficient to enable the reactions under the 
trusses and the horizontal component of cable tension to be found. 

One of the best methods of procedure for such cases is that 
of least work, in which the horizontal component of cable ten- 
sion is so found that the total work performed in the elastic 
deflection of the stiffening trusses, suspension-rods, cables, and 
towers is a minimum. After having found this horizontal com- 
ponent of the cable tension and the reactions under the stiffening 
trusses, the stresses in all the members of the entire structure 
can be at once determined. It is obvious that the stiffening 
truss and the cables must deflect together. It is equally evident 
that the deeper the stiffening trusses are the more load will be 
required to deflect them to any given amount, and hence that 
the deeper they are the more load they will carry independently 
of the cable. It is desirable to throw as much of the duty of 
carrying loads upon the cables as possible. It therefore follows 
that the stiffening trusses should be made as shallow as the proper 
discharge of their stiffening duties will permit. 

137. Stresses in Cables and Moments and Shears in Trusses. — 
The necessary limits of this discussion will not permit even the 
simplest analyses to be given. It is evident, however, that the 
greatest cable stresses will exist at the tops of the towers, and 
that if the horizontal component of cable tension be found by 
any proper method, the stress at any other point will be equal 
to that horizontal component multiplied by the secant of cable 
inclination to a horizontal line, it being supposed that the sus- 
penders are found in a vertical plane. 

If the stiffening trusses are jointed at the centre of the main 
span, as well as at the ends, the simple equations of statical 
equilibrium are sufficient in number to make all computations, 
for the reason that the centre pin- joint gives the additional con- 
dition that, whatever may be the amount or distribution of 
loading, the centre moment must be zero. If / is the length of 



STRESSES IN CABLES AND MOMENTS IN TRUSSES. 175 

main or centre span and p the moving load per linear foot of span, 
and if the stiffening trusses run from tower to tower, the follow- 
ing equations will give their greatest moments and shears both 
by the old and new theory of the stiffening truss. 

/ = load per lin. ft., /=length of span in ft., 

Old theory. Isew theory. 

Max. moment.. . . 71/ = 0.01856^/^ M = o.oi6s2pP] no centre 

Max. shear 5= ^pl S = l-pl ) hinge. 

With centre hinge ill -=0.01883/?/^ and S = lpl 

The details of the theory of stiffening trusses for suspension 
bridges have been well developed during the past few years and 
are fully exhibited in modern engineering literature. The long 
spans requiring stiffened suspension bridges are usually found 
over navigable streams, and hence those bridges must be placed 
at comparatively high elevations. This is illustrated by the 
clear height of 135 feet required under the East River suspension- 
bridge structures already completed and in progress. Further- 
more, the heights of towers above the lowest points of the cables 
usually run from one eighth to one twelfth of the span. These 
features expose the entire structure to comparatively high wind 
pressures, which must be carefully provided against. This is 
done by the requisite lateral bracing between the stiffening 
trusses and by what is called the cradling of the cables. The 
latter expression simply means that the cables as they are built 
are swung out of a vertical plane and toward the axis of the 
structure, being held in that position by suitable details. The 
cables on opposite sides of the bridge are thus moved in toward 
each other so as to produce increased stability against lateral 
movement. Occasionally horizontal cables are stretched be- 
tween the towers in parabolic curves in order to resist horizontal 
pressures, just as the main cables carry vertical loads. This 
matter of stability against lateral wind pressures requires and 
receives the same degree of careful consideration in design as 
that accorded to the effects of vertical loading. The same gen- 
eral observation applies also to the design of the towers. 

138. Thermal Stresses and Moments in Stiffened Suspension 
Bridges. — All material used in engineering structures expands 



176 BRIDGES. 

and contracts with rising and falling temperatures to such an 
extent that the resulting motions must be provided for in struc- 
tures of considerable magnitude. In ordinary truss-bridges one 
end is supported upon rollers, so that as the span changes its 
length the truss ends move the required amount upon the rollers. 
In the case of stiffened suspension bridges, however, the ends of 
the cables at the anchorages are rigidly fixed, so that any adjust- 
ment required by change of temperature must be consistent with 
the change of length of cable between the anchorages. The 
backstays, which are those portions of the cables extending from 
the anchorages to the tops of the towers, expand and contract 
precisely as do the portions of the cable between the tops of the 
towers. As the cables lengthen, therefore, the sag or rise at the 
centre of the main span will be due to the change in the entire 
length of cable from anchorage to anchorage. In order to meet 
this condition it is usual to support the cables at the tops of the 
towers on seats called saddles which rest upon rollers, so as to 
afford any motion that may be required. Designs have been 
made in which the cables are fixed to the tops of steel towers. In 
such cases changes of temperature would subject the towers to 
considerable bending which would be provided for in the design. 

The rise and fall at the centres of long spans of stiffened sus- 
pension bridges is considerable; indeed, for a variation of 120° 
Fahr. the centre of the New York and Brooklyn Bridge changes 
its elevation by 4.6 feet if the saddles are free to move, as intended. 
In the case of a stiffened suspension bridge designed to cross the 
North River at New York City with a main span of 3200 feet 
a variation of 120° Fahr. in temperature would produce a change 
of elevation of the centre of the span of 6.36 feet. Such thermal 
motions in the structure obviously will produce stresses of con- 
siderable magnitude in various parts of the stiffening trusses, all 
of which are invariably recognized and provided for in good 
design. 

139. Formation of the Cables. — At the present time suspen- 
sion-bridge cables are made by grouping together in one cylindrical 
mass a large number of so-called strands or individual small cables, 
each composed of a large number of parallel wires about one 
sixth of an inch in diameter. The four cables of the New York 



ECONOMICAL LIMITS OF SPANS. ' 177 

and Brooklyn Bridge are each composed of 19 strands, each of 
the latter containing 332 parallel wires, making a total of 6308 
wires, the cables themselves being 15^ inches in diameter. The 
wire is No. 7 gauge, i.e., 0.18 inch in diameter. In the new East 
River Bridge each of the four cables is 18^ inches in diameter 
and contains 37 strands, each strand being composed of 208 
wires all laid parallel to each other, or a total of 7696 wires. The 
size of the wire is No. 6 (Roebling) gauge, i.e., 0.192 inch in diam- 
eter. These strands are formed by laying wire by wire, each in 
its proper place. The strands are then bound together into a 
single cable, around which is tightly wound a sheathing or casing 
of smaller wire, 0.134 inch in diameter for the New York and 
Brooklyn Bridge. The tightness of this binding wire insures the 
unity of the whole cable, each wire having been placed in its origi- 
nal position so as to take a tension equal to that of each of the 
other wires. The suspension-rods are usually of wire cables and 
are attached by suitable details to the lower chords of the stiffen- 
ing truss, also by specially designed clamps to the cable. The 
stiffening trusses are usually built with all riveted joints, so as to 
secure the greatest possible stiffness from end to end. The 
stiffened suspension bridge has been shown by experience, as 
well as by theory, to be well adapted to carry railroad traffic 
over long spans. 

140. Economical Limits of Spans. — In the past, suspension 
bridges have, in a number of cases, been built for comparatively 
short spans, but it is well recognized among engineers that their 
economical use must be found for spans of comparatively great 
length. While definite lower limits cannot now be assigned to 
such spans, it is probable that with present materials of con- 
struction and with available shop and mill capacities the ordi- 
nary truss-bridge may be economically used up to spans approxi- 
mately 700 to 800 feet, and that above that limit the cantilever 
system is economically applicable to lengths of span not yet 
determined but probably between 1600 and 2000 feet. The 
special field of economical employment of the long-span stiffened 
suspension bridge will be found at the upper limit of the canti- 
lever system. So far as present investigations indicate, the 
stiffened suspension type of structure may be employed to 



178 BRIDGES. 

advantage from about 1800 feet up to the maximum practicable 
length of span not yet assignable, but perhaps in the vicinity of 
4000 feet. Obviously such limits are approximate only and 
may be pushed upward by further improvements in the produc- 
tion of material and in the enlargement of both shop and mill 
capacity. 



PART III. 

WATER-WORKS FOR CITIES AND TOWNS. 



CHAPTER XIV. 

141. Introductory. — A preceding lecture in this course has 
shown to what an advanced state the pubHc supply of water to 
large cities was developed in ancient times. The old Romans, 
Greeks, Egyptians, and other ancient peoples evidently posesssed 
an adequate appreciation of the value of efficient systems of 
public water-supply. Very curiously that appreciation dimin- 
ished so greatly as almost to disappear during the middle ages. 
The demoralization of public spirit and the decrease of national 
power which followed the fall of Rome induced, in their turn, 
among other things, a neglect of the works of the great water 
system of Rome, entailing their partial destruction. The same 
retrogression in civilization seemed to affect other ancient nations 
as well, until probably the lowest state of the use of public waters 
and the construction of public water systems was reached some- 
where between a.d. iooo and a.d. 1300 or 1400. Without 
reasonable doubt the terrible epidemics or plagues of the middle 
ages can be charged to the absence of suitable water-supplies 
and affiliated consequences. During that middle period of the 
absence of scientific knowledge and any apparent desire to ac- 
quire it, sanitary works and consequently sanitary conditions of 
life were absolutely neglected. No progress whatever was made 
toward reaching those conditions so imperative in large centres 
of population for the well-being of the community. Grossly 
polluted waters were constantly used for public and private sup- 
plies, and no efforts whatever were made among the masses 

179 



180 WATER-WORKS FOR CITIES AND TOWNS. 

toward the suitable disposition of refuse matters or, in a word, 
to attain to sanitary conditions of living. 

A few important works were completed, particularly in Spain, 
but nothing indicative of general relief from the depths of igno- 
rance and sanitary demoralization to which the greater portion 
of the civilized world had sunk at that time. The city of Paris 
took all its water from the Seine, except that which was supplied 
by a small aqueduct built in 1183. So small was the supply, 
aside from the water obtained from the river, that in 1550 it is 
estimated that the former amounted to about one quart only 
per head of population per day. The situation in London was 
equally bad, for it was only in the first half of the thirteenth 
century that spring-water was brought to the city by means of 
lead pipes and masonry conduits. Public water-works began 
to be constructed in Germany on a small scale in the early part 
of the fifteenth century. Obviously no pumps were available 
in those early days of water-supply, so that the small systems 
which have been mentioned were of the gravity class; that is, 
the water flowed naturally in open or closed channels from its 
sources to the points of consumption. Pumps of a simple and 
crude type first began to be used at a point on the old London 
Bridge in 1582, and in Hanover in 1527. Subsequently to those 
dates other pumps were set up on London Bridge, and installa- 
tions of the same class of machinery were made in Paris in 1608, 
usually operated by water-power in some simple manner, as by 
the force of the water-currents. In 1624 the Paris supply re- 
ceived a reinforcement of 200,000 gallons per day by the comple- 
tion of the aqueduct Arcueil. The New River Company was 
incorporated in 16 19 for the partial supply of the city of London, 
and it began to lay its pipes at that time. As its name indicates, 
it took its supply fro-n New River, and the inception of its busi- 
ness is believed to mark the first application of the principle of 
supplying each house with water. This company is still in exist- 
ence and furnishes a considerable portion of the present London 
supply. 

142, First Steam-pumps. ^ The application of steam to the 
creation or development of power by Watt, near the end of the 
eighteenth century, stimulated greatly the construction of water- 



WATEB-SUPPLY OF PARIS AXD LONDON. 181 

works, as it offered a very convenient and economical system of 
pumping. It seems probable that the first steam-pumps were 
used in London in 1761. Twenty years later a steam-pump was 
erected in Paris, while another was installed in 1783. The second 
steam-pump in London was probably constructed in 1787. In 
all these earlier instances of the use of steam-pumps river supplies 
were naturally used. 

143. Water-supply of Paris and London. — After the early 
employment of steam pumping-machinery demonstrated its 
great efficiency for public water-supplies, the extension of the 
latter became more rapid, and since 1800 the supplies of the two 
great cities of London and Paris have been greatly increased. 
As late as 1890 the Paris supply amounted to about 65 gallons 
per head of population, one fourth of which was used as potable, 
being drawn from springs, while three fourths, drawn from rivers, 
was used for street-cleaning or'other public purposes. This sup- 
ply, however, was found inadequate and was re-enforced in 1892 
by an addition of 30,000,000 gallons per day of potable water 
brought to the city by an aqueduct 63 miles long. Another 
addition of about 15,000,000 gallons has been provided more 
recently. 

Rather curiously the water-supply of London is afforded by 
eight private companies, one of which is the old New River 
Company already mentioned. These companies, with one excep- 
tion, draw their supply mainly from the rivers Thames and Lea, 
all such water being filtered. The remaining company draws 
its water from deep wells driven into the chalk. The total popu- 
lation supplied amounts to about 5,500,000, the rate of supply 
being thus less than 45 gallons per head per day. 

144. Early Water-pipes. — Inasmuch as the use of cast iron 
for pipes was only begun about the year 1800, other materials 
were used prior to that date. As is well known, the pipes used 
in ancient water-works were either of lead or earthenware. In 
the eighteenth century wooden pipes made of logs with their cen- 
tres bored out were used, sometimes 6 or 7 inches in diameter. 
As many lines of these log pipes were used as needed to conduct 
a single line of supply. In the earlier portion of the nineteenth 
century such log pipes, usually of pine or spruce, were used by 



182 WATER-WORKS FOR CITIES AND TOWNS. 

the old Manhattan Company for the supply of New York City. 
A section of such a wooden pipe, with a bore of about 2^ inches 
is preserved in the museum of the Department of Civil Engineer- 
ing of Columbia University. Large quantities of such pipes 
were formerly used. 

145. Earliest Water-supplies in the United States. — The earli- 
est system of public water-supply in this country was completed 
for the city of Boston in 1652. This was a gravity system. It is 
believed that the first pumping-machinery for such a supply was 
set up for the town of Bethlehem, Pa., and put in operation in 
1754. Subsequently water-supplies were completed for Provi- 
dence, R. I., 1772, and for Morristown, N. J., in 1791 ; the latter 
has maintained a continuous existence since that date. The 
first use of steam pumping-machinery in this country was in 
Philadelphia in 1800. This machinery, curiously enough, was 
largely of wood, including some portions of the boiler; it was 
necessarily very crude and would perform with 100 pounds of 
coal only about one twenty-fifth or one thirtieth of what may 
be expected from first-class pumping-machinery at the present 
time. Other cities and towns soon began to follow the lead of 
these earlier municipalities in the construction of public water- 
supplies, but the principal development in this class of public 
works has taken place since about 1850. 

It is estimated that the total population supplied in 1880 was 
about 12,000,000, which rose to about 23,000,000 in 1890, and it 
is probably not less than 50,000,000 at the present time. 

146. Quality and Uses of Public Water-supply. — Advances in 
the public supplies in this country have been made rather in the 
line of quantity than quality. Insufficient attention has been 
given both to the quality of the original supply and to the char- 
acter of the reservoirs in which it is gathered until within possibly 
the past decade. A few cities like Boston have scrutinized with 
care both the quality of the water and the character of the bot- 
tom and banks of reservoirs, and have spared neither means nor 
expense to acquire a high degree of excellence in their potable 
water. The same observations can be applied to a few other 
large cities, but to a few only. The realization of the dependence 
of public health upon the character of water-supply, however, 



AMOUNT OF PUBLIC WATER-SUPPLY. 183 

has been rapidly extending, and it will doubtless be but a short 
time before the care exercised in collecting and preparing water 
for public use will be as great in this country as in Europe, where 
few large cities omit the filtration of public waters. 

The distribution of water supplied for public use is not limited 
,to domestic purposes, although that class of consumption con- 
trols public health so far as it is affected by the consumption of 
water. The applications of water to such public purposes as 
street-cleaning and the extinguishing of fires are of the greatest 
imiportance and must receive most careful consideration. Again, 
the so-called system of water-carriage in the disposal of domestic 
and manufacturing wastes, constituting the field of sewage-dis- 
posal, depends wholly upon the efficiency of the water-supply. 

147. Amount of Public Water-supply. — The first question 
confronting an engineer in the design of public water-supply is 
the amount which should be provided, usually stated on the basis 
of an estimated quantity per head of population. This is not 
in all cases completely rational, but it is by far the best basis 
available. If the water-supply is designed for a small city or 
town previously supplied by wells or other individual sources, 
the first year's consumption will be low per head of population 
for the reason that many people will retain their own sources 
instead of taking-^ share of the public supply. As time elapses 
that portion of population decreases quite rapidly in numbers, 
and in a comparatively few years practically the whole population 
will use the public supply. In communities, therefore, where 
public systems have long existed and it is desired either to add 
to the old supply or to install new ones, the only safe basis of 
estimate is the entire population. 

148. Increase of Daily Consumption and the Division of that 
Consum.ption. — The amount of Avater required per head of popu- 
lation might naturally be assumed identical with the past con- 
sumption, but that would frequently be incorrect. It is one of 
the most prominent features of the history of public w^ater-sup- 
plies in this country that the consumption per head of population 
has increased with great rapidity from the early years of the 
installation of the different systems, for reasons both legitimate 



184 WATER-WORKS FOR CITIES AND TOWNS. 

and illegitimate. The daily average consumption of water from 
the Cochituate Works of the Boston supply increased from 42 
gallons per head of population in 1850 to 107 gallons in 1893, 
and in the Mystic Works of the same supply the increase was 
from 27 gallons in 1865 to 89 gallons in 1894. Again, the daily 
average consumption in Chicago rose from 43 gallons per head 
per day in i860 to 147 gallons in 1893, while in Philadelphia 
during the same period the increase was from 36 gallons per 
head per day to 150 gallons. In Cambridge, Mass., the increase 
in daily average consumption per head of population was from 
44 gallons in 1870 to 70 gallons in 1894. These instances are 
sufficient to show that, under existing conditions, the daily con- 
sumption was increased at a rapid rate in the cities named, and 
they have been selected as fairly representative of the whole 
field. Civil engineers have made extended studies in connec- 
tion with this question in a great number of cities, for it bears 
upon one of the most important lines of public works. It is 
absolutely essential to the health and business prosperity of 
every city that the water-supply should be abundant, safe, and 
adapted to the industrial and commercial pursuits of its popula- 
tion. It is imperative, therefore, that the division of the daily 
supply should be carefully analyzed. For this purpose the 
water-supply of a city may be, and frequently is, divided into 
four parts: 

(i) That used for domestic purposes; 

(2) That used for commercial and industrial purposes; 

(3) That used for public purposes ; 

(4) That part of the supply which is wasted. 

I. That portion of the supply consumed for domestic pui'- 
poses includes not only the water used in private residences, 
but in those branches of consumption which may be considered 
of a household character found in hotels, clubs, stores, markets, 
laundries, and stables, or for any other residential service. As 
might be expected, this branch of consumption varies largely 
from one city to another. The results of one of the most inter- 
esting and suggestive studies ever made in connection with this 
subject are given by Mr. Dexter Brackett, M. Am. Soc. C. E., in 



INCREASE OF DAILY CONSUMPTION. 185 

the Transactions of the American Society of Civil Engineers for 
1895. In Boston the purely domestic consumption varied in 
different houses and apartments from 59 gallons per head per 
day in costly apartments down to 16.6 gallons per head per day 
in the poorest class of apartment. In Brookline, one of the 
finest suburbs of Boston, the quantity was 44.3 gallons per 
day. In some other cities of Massachusetts, as Newton, Fall 
River, and Worcester, this class of consumption varied from 
6.6 gallons to 26.5 gallons per day, the latter quantity being 
found at Newton in some of the best residences, and the former 
at houses also in Newton having but one faucet each. In Yon- 
kers, N. Y., where the system was metered, the amount was 
21.4 gallons per head of population per day, while in portions 
of London, England, it varied from 18.6 to 25.5 gallons per head 
per day. The average of these figures gives a result of 18.2 
gallons per head per day, which, in round numbers, may be put 
at 20 gallons. 

2 . It is obvious that the rate of consumption for commercial 
and industrial purposes in any city must vary far more than 
that for domestic purposes, for the reason that some cities may 
be essentially residential in character while others may be essen- 
tially manufacturing. At the same time, it is to be remembered 
that many manufacturing establishments may have their own 
water-supply. The city of Fall River, Mass., is eminently a 
manufacturing city, yet Mr. Brackett found that the manufac- 
turing demand on the public water-supply amounted to 2 gallons 
only per inhabitant per day, as the manufacturers draw the most 
of their supply from the river, but that where the manufacturers 
depend upon the public supply for all their water the amount 
rises to a value between 20 and 30 gallons per inhabitant. In 
Boston in 1892 the water consumed for all manufacturing and 
industrial purposes, including railroads, gas-works, elevators, 
breweries, etc., amounted to 9.24 gallons per head of popula- 
tion per day, while in Yonkers in 1897 the total consumption 
for commercial purposes was 27.4 gallons per head per day. In 
the city of New York, as nearly as can be estimated, the consump- 
tion for commercial purposes is probably not far from 25 gallons 



186 WATER-WORKS FOR CITIES AND TOWNS. 

per inhabitant per day. Reviewing all these results, it may be 
stated that the water consumption for commercial and indus- 
trial purposes will generally range from lo to 30 gallons per 
inhabitant per day. 

3 . The consumption of water for public purposes is a smaller 
amount than either of the two preceding. It covers such uses 
as public buildings, schools, street-sprinkling, sewer-flushing, 
fountains, fires, and other miscellaneous objects, more or less 
similar to those just named. The total use of this character 
was 3.75 gallons per inhabitant per day for Boston in 1892, 
and 5.57 gallons per inhabitant per day for Fall River in 1899. 
A few other cities give the following results: Minneapolis in 
1897, 5 gallons; Indianapolis, 3 gallons; Rochester, N. Y., 3 
gallons; Newton, Mass., 4 gallons; Madison, Wis., 10 gallons. 
In Paris it is estimated that not far from 2 . 5 gallons per head of 
population per day are used. It is probable, therefore, that an 
amount of 5 gallons per day per inhabitant will cover this partic- 
ular line of consumption. 

4. A substantial portion of the water-supply of every city 
fails to serve any useful purpose, for the reason that it runs to 
waste either by intention or by neglect. The sources of this 
waste are defective plumbing, including leaky faucets and cocks ; 
deliberate omission to close faucets and cocks, constituting wilful 
waste; defective or broken mains, including leaky joints; and 
waste to prevent freezing. 

149. Waste of Public Water. — All these wastes except the 
last are inexcusable. There is no difficulty in detecting defective 
plumbing, and its existence is generally known to the householder ; 
but if the wasted water is not measured and paid for, it is far too 
frequently considered more economical to continue the waste 
than to pay for the plumber's services. In a multitude of cases 
cocks are left open indefinitely for all sorts of insignificant reasons ; 
in closets, under the erroneous impression that the continuous 
running of the stream will materially aid in a more efi'ective 
cleansing of soil- and sewer-pipes, failing completely to appre- 
ciate that a far more powerful stream is required for that purpose ; 
sometimes in sinks, for refrigerating purposes, and in many other 



WASTE OF PUBLIC WATER. 187 

inexcusably wrong ways. These sources of wilful waste lead to 
large losses and constitute one of the most unsatisfactory phases 
of administration of a public water system. Such losses result 
in a vicious waste of public money. The amount of water flow- 
ing from leaky joints and from leaks in pipes and mains is neces- 
sarily indeterminate because it escapes without evidence at the 
surface except in rare cases. In every instance where examina- 
tions have been made and a careful record kept of the amount 
of water supplied to a city, it has been found that the aggregate 
of the measured amounts consumed fail nearly to equal the total 
supply. There are probable errors both in the measurement 
of the quantities supplied and in the quantities consumed, but 
the large discrepancy cannot be accounted for in this manner. 
In many cases consumed water has even been carefully measured 
by meters, as at Yonkers, New York, Newton, Milton, and Fall 
River, Mass., Madison, Wis., and at other places, but yet the 
discrepancy appears to be nearly as wide as ever. Again, in 
1893 observations were carefully made on the consumption of 
the water received by the Mystic supply of the Boston system 
at all hours of the twenty-four. Obviously between i and 4 a.m. 
the useful consumption should be nearly nothing, but, on the 
contrary, it was found to be nearly 60 per cent, of the average 
hourly consumption for the entire twenty-four hours. The 
waste at Buffalo, N. Y., in 1894 was estimated at 70 per cent of 
the total supply. Similar observations in other places have 
given practically the same results. It has also been found that, 
in a number of instances, where old watercourses have been 
completely obliterated by considerable depths of filling required 
by the adopted grades of city streets and lots, and excavations 
for buildings have subsequently been opened practically the 
full volume of the former streams are flowing along the original 
but filled channel. This result has been observed under a prac- 
tically impervious paved city surface. It is difficult to imagine 
the source of such a supply except from defective pipe systems 
or sewers. A flow of a least 100,000 gallons per day from a 
broken pipe which found its way into a sewer has also been dis- 
covered without surface evidence. These and man}^ other 
results of experience conclusively demonstrate that much water 



188 WATER-WORKS FOR CITIES AND TOWNS. 

flows to waste unobserved from leaky joints and defective or 
broken pipes. 

Inasmuch as cast-iron water-pipes are produced in lengths 
which net 12 feet as laid, there will be at least 440 joints per mile. 
Furthermore, as leaky joints and broken pipes are as likely to 
occur at one place as another, it seems reasonable to estimate 
leakage through them as proportionate to the length of the pipe- 
line in a system; and that conventional law is frequently as- 
sumed. New pipe-lines have sometimes shown a leakage of 
500 to 1200 gallons per mile of line per day. Civil engineers 
have sometimes specified the maximum permissible leakage of 
a new pipe-line at 60 to 80 gallons per mile of line per day for 
each inch in diameter of pipe, thus permitting 600 to 800 gallons 
to escape from a lo-inch pipe. In 1888 the late Mr. Chas. B. 
Brush reported a leakage of about 6400 gahons per mile per day 
from a practically new 24-inch cast-iron main, 11 miles long, of 
the Hackensack Water Company, the pressure being no pounds 
per square inch. Tests of water-pipes in German and Dutch 
cities have been reported as showing less waste than 300 gallons 
per mile per day, but such low results, unless for very low pres- 
sures and short lines, may reasonably be doubted. Obviously 
losses of this character will probably increase with the age of 
the pipe. By a very ingenious procedure based upon his own 
experience, Mr. Emil Kuichling of Rochester, N. Y., reaches 
the conclusion that a reasonable allowance for the waste from 
leaky joints and defective pipes is 2500 to 3000 gallons per mile 
of cast-iron pipe-line per day. If, as is frequently the case, the 
population per mile of pipe ranges from 300 to 1000, the preced- 
ing allowance amounts to 3 to 10 gallons per head of population 
per day. The loss or waste due to running cocks or faucets to 
prevent freezing cannot be estimated with sufficient accuracy 
to receive a definite valuation, but it must be considered an ele- 
ment of the total item of waste. 

150. Analysis of Reasonable Daily Supply per Head of Popula- 
tion. — It has repeatedly been found that the losses or wastes set 
forth in the preceding statements amount apparently to quanti- 
ties varving from 30 to 50 per cent of the total supply; or, to put 
it a little differently, the water unaccounted for in even the best 



ACTUAL DAILY CONSUMPTION IN AMERICAN CITIES. 189 

systems now constructed apparently may reach one third to one 
half of the total supply. This is an exceedingly wasteful and 
unbusinesslike showing. It is probable that the statement is, 
to some extent at least, an exaggeration. It is practically certain 
that either the amount supplied or the amounts consumed, or 
both, are never measured with the greatest accuracy, and that 
the errors are such as generally swell the apparent quantity 
wasted. After making judicious use of the data thus afforded 
by experience, it is probable that the following tabular state- 
ment given by Messrs. Turneaure and Russell represents limits 
within which should be found the daily average supply of water 
in a well-constructed and well-administered svstem. 



Use. 


Gallons per Head per Day. 


Minimum. 


Average. 


Maximum. 


Domestic 

Industrial and commercial.. 

Public 

Waste 


15 

5 

3 

15 


25 
20 

5 
25 


40 

35 
10 

30 


Total 


38 


75 


115 



The values given in the preceding table are reasonable and 
sufficient to supply the legitimate needs of any community, but, 
as will be shown in the succeeding table, there are cities in this 
country whose average consumption is more than twice the 
maximum rate given above. 

151. Actual Daily Consumption in Cities of the United States. — 
The following table exhibits the average daily consumption of 
water throughout the entire year for the cities given, as deter- 
mined for the years indicated in the table. 

The city of Buffalo shows a daily consumption of 271 gallons 
per inhabitant, and Allegheny, Pa., 247 gallons per inhabitant. 
There are a considerable number showing an average daily con- 
sumption per inhabitant of 160 gallons or more. All such high 
averages exhibit extravagant use of water, or otherwise ineffi- 
cient administration of the water-supply. The reduction of 
such high rates of consumption is one of the most difficult prob- 
lems confronting the administration of public works. The use 



190 



WATER-WORKS FOR CITIES AND TOWNS. 
TABLE I. 



Population. 



1890. 



NeAV York i 

Chicago 'i 

Philadelphia. j i 

Brooklyn 

St. Louis 

Boston 

Cincinnati 

San Francisco 

Cleveland 

Buffalo 

New Orleans 

Washington 

Montreal 

Detroit 

Milwaukee 

Toronto 

Minneapolis 

Louisville 

Rochester 

St. Paul 

Providence 

Indianapolis 

Allegheny 

Columbus 

Worcester 

Toledo 

Lowell 

Nashville 

Fall River 

Atlanta 

Memphis 

Quebec 

Dayton, O 

Camden, N. J 

Des Moines, la 

Ottawa, Ont 

Yonkers, N. Y 

Newton, Mass 

Madison, Wis 

Albany, N. Y 

New Bedford, Mass . . 

Springfield, Mass 

Holyoke, Mass 



-515.301 
,099-850 
,046,964 

838-547 
451-770 
448,477 
305,891 
298,997 
270,055 
255,664 
242,039 

230,392 
216,000 
205,876 
204,468 
181,000 
164,738 
161,129 
133,896 
133,156 
132,146 

105,436 
105,287 
88,150 
84,655 
81,434 
77,696 
76,168 
74-398 
65,533 
64,495 
63,000 
61,220 
58,313 
50,093 
44,000 

32,033 
24,379 
13,426 
98,000 
55,000 
49,299 
40,000 



Popula- 
tion 
per Tap 



Per Cent 
of Taps 
Metered 



13-9 
7-1 
6.1 
8.7 

II. 8 
6.6 

8.5 
9.9 
8.7 

6.3 
54-0 

6.5 
5-3 
5-1 

II . I 
4.0 

16.5 



5-4 
12.7 

9-4 
35-6 

7.0 

II-5 
8.9 

18.6 
9.2 

14. 

14- 

20 . 

II . 

10 . 

20. 



20. o 

4-2 

12.0 

5-5 
II .0 



2-5 

0.3 

2-5 
8.2 

5-0 
4.1 
41 .4 
5-8 
0.2 

0.4 
0.3 
1-7 
2 . 1 

31-9 
4.1 

6.3 

5-9 
II. 4 

4.2 
62 .4 

7.6 

o 

6.4 
89.4 

9-4 
22 .9 

0.8 
74.6 
89.6 

3-7 

o 

3-8 



60.0 

o 
82.4 
67.4 
31.0 

0.4 



1890. 



79 
140 
132 

72 

72 

80 
112 

61 
103 
186 

37 
158 

67 
161 
no 
100 

75 
74 
66 
60 
48 
71 
238 
78 

59 
72 
66 

146 
29 
36 

124 

160 
47 

131 
55 

130 
68 
40 
40 

162 

99 

87 
77 



Per Cent 
of Taps 
Metered 



1895. 



27 .0 
2.8 
0.74 
1.9 
7-4 
5-2 

6.5 
28.0 

4.5 
0.85 



1-5 
1.6 
8.2 

51-0 
3-7 

16 .0 
6.6 

18.0 

1-7 

74.0 

7-1 

7-1 

9-3 

90.0 

35-0 
33 -o 
24 .0 
82.0 
99 -o 

4.6 

o 
24.0 

o 
42 .6 

o 
59.8 

77-3 
61 .0 
12.3 
154 
319 
5.82 



a o 



5i >" 

1895. 



100 

139 
162 

89 

98 

100 

35 

63 

142 

271 

35 
200 

83 
152 

lOI 

100 
88 
97 
71 
60 

57 
74 

247 

127 

66 

70 

82 

139 

35 

42 

100 

170 

50 

200 

43 
200 
100 

65 

52 



o.t; fi 
1900. 



115 
190 
229 

III 

143 
121 

73 
175 
262 

48 
174 

156 
84 

93 

83 
51 
54 
79 

183 
67 

59 

83 

140 

35 
61 



62 

185 
48 

76 
62 

44 
192 

lOI 

88 
io3=f 



* Estimated. 

of the meter has proved most efficient in preventing wastes or 
other extravagant consumption, as in that case every consumer 
pays a prescribed rate for the amount which he takes. 



ACTUAL DAILY CONSUMPTION IN FOREIGN CITIES. 



191 



152. Actual Daily Consumption in Foreign Cities. — It has 
been for a long time a well-recognized fact that the daily use of 
water in American municipalities is far greater per inhabitant 
than in European cities. It is difficult to explain the marked 

TABLE II. 



City. 



Estimated 
Population. 



Consumption 

per Capita 

Daily, 

Gallons. 



England, 1896-97:* 

London 

Manchester 

Liverpool 

Birmingham 

Bradford 

Leeds 

Sheffield 

Nottingham 

Brighton 

Plymouth 

Germany, 1890 (Lueger) : 

Berlin -. . 

Breslau 

Cologne 

Dresden 

Diisseldorf 

Stuttgart 

Dortmund 

Wiesbaden 

France, 1892 (Bechmann) : 

Paris 

Marseilles 

Lyons . 

Bordeaux 

Toulouse .- 

Nantes 

-Rouen 

Brest 

Grenoble 

Other countries, 1892-96 (Bechmann): 

Naples 

Rome 

Florence 

Venice 

Zurich 

Geneva 

Amsterdam 

Rotterdam 

Brussels 

Vienna 

St. Petersburg 

Bombay 

Sidney 

Buenos Avres 



,700,000 
849,093 
790,000 
680,140 
436,260 
420,000 
415,000 
272,781 
165,000 
98,575 

,427,200 
330,000 
281,700 
276,500 
144,600 
139,800 
89,700 
62,000 

!, 500, 000 
406,919 
401,930 
252,654 
148,220 
125,000 
107,000 

70-778 
60,855 

481,500 

437.419 

192,000 

130,000 

80,000 

70,000 

515,000 

240,000 

489,500 

[,365,000 

960,000 

810,000 

423,600 

680,000 



42 
40 

34 
28 

31 
43 
21 
24 
43 
59 



20 

34 
21 

25 
26 
78 
20 

53 

202 

31 
58 
26 

13 

32 

3 

264 

53 
264 
21 
II 
60 
61 
20 

53 
20 
20 
40 
61 
38 
34 



* Compiled, except the figures for London, by Hazen. Engineering News, 1899, xli. p. iii. 



192 WATER-WORKS FOR CITIES AND TOWNS. 

difference, but it is probably due in large part to the more extrav- 
agant general habits of the American people. Examinations 
in a number of cases have shown that the actual domestic use 
of water, at least in some of the American cities, is not very 
different from that found in corresponding foreign cities. Table 
1,1 exhibits the consumption of water in European cities, as 
compiled from various sources and given Ijy Turneaure and 
Russell. 

These foreign averages, with three exceptions, represent 
reasonable quantities of water used, and they have been con- 
firmed as reasonable by many special investigations made in 
this country. 

153. Variations in Rate of Daily Consumption. — The preced- 
ing observations are all based upon an average total consumption 
found by dividing the total annual consumption by the number of 
days in the year. This is obviously sufficient in a determination 
of the total supply needed, but it is not sufficient in those matters 
which involve a rate of supply during the different hours of the 
day, or the amount of the supply for the summer months as com- 
pared with those of the winter. As a general rule the greatest 
supply will be required during the hot summer months when 
lawn- and street-sprinkling is most active. It appears from 
observations made in a considerable number of the large cities 
of the United States that the maximum monthly average con- 
sumption may run from about no to nearly 140 per cent of the 
monthU^ average throughout the year. As an approximate 
value only, it may be assumed for ordinary purposes that the 
maximum monthly demand will be 125 per cent of the average. 

The daily rate taken throughout the year is considerably 
more variable than the monthly. There are days in some por- 
tions of the year when consumption by hotels and industrial 
activities is at a minimum. On the other hand, there are other 
days when those activities are at a maximum and the total draft 
will be correspondingly high. Experience has shown that the 
maximum total draft may vary from about 115 to nearly 200 
per cent of the average. It is permissible, therefore, to take 
approximately for general purposes the maximum total daily con- 
sumption as 150 per cent of the average. Manifestly any total 



SUPPLY OF FIRE-STREAMS. 193 

consumption will have an hourly rate which may vary greatly 
from the early morning hours, when the draft should be almost 
nothing, to the forenoon hours on certain days of the week, when 
the draft is a maximum. These variations have frequently been 
investigated, and it has been shown that the maximum rate per 
hour of a maximum day may sometimes rise higher than 300 
per cent of the average hourly rate for the year. These consid- 
erations obviously attain their greatest importance in connection 
with the capacity of the plant, either power or gravity, from 
which the city directly draws its supply. The hourly capacity 
of the pumps or steam-plant furnishing the supply need not neces- 
sarily be equal to the maximum, since storage -reservoirs may 
be and usually are used; but the capacity of the pipe system 
leading from such storage-reservoirs must be equal to the miaxi- 
mum hourly rate required. 

154. Supply of Fire-streams.-— The draft on a water-supply 
for fire-extinguishing purposes may have an important influence 
upon the hourly rate of consumption. These observations are 
particularly pertinent in connection with the water-supply of 
small cities where the draft of fire-engines may be considered a 
large percentage of the total hourly consumption. It is obviously 
impossible to assign precisely the number of fire-streams which 
may be required simultaneously in a city having a. given popu- 
lation, but experiences of a considerable number of civil engineers 
furnish reasonable bases on which such estimates may be made. 
Table III exhibits such estimates as made by the civil engineers 
indicated. It is given by Mr. Emil Kuichling in the Transactions 
of the American Society of Civil Engineers for December, 1897. 
Probably no more reasonable estimate can be now presented. 

The discharge of each fire-stream will of course vary with 
its diameter and the pressure at the fire-engine, but as an average 
it is reasonable to assume that each stream will discharge 250 
gallons per minute. The quantity of water required, therefore, 
to supply the estimated number of streams given in Table III 
is found by simply multiplying the number of those streams 
by 250, to ascertain the total number of gallons consumed per 
minute. If x is the number of thousand inhabitants in any 
city, and if y represents the required number of streams, then 



194 



WATER-WORKS FOR CITIES AND TOWNS. 



TABLE III. 

TABLE EXHIBITING ESTIMATED NUMBER OF FIRE-STREAMS REQUIRED SIMUL- 
TANEOUSLY IN AMERICAN CITIES OF VARIOUS MAGNITUDES. 



Population of 


Number of Fire-streams Required Simultaneously. 


Community. 


I 

Freeman. 


2 

Shedd 


3 
Fanning. 


4 
Kuichling. 


1 ,000 


2 to 3 






3 
6 


4,000 

5,000 

10,000 

20,000 




7 


4 to 8 

6 to 12 

8 to 15 
12 to 18 


5 

7 

10 

14 


6 


10 


9 


40,000 
50,000 
60,000 




18 


14 


20 


15 to 22 
20 to 30 


17 

22 




100,000 
150,000 
180,000 


18 

25 


23 
34 
38 
40 

44 
48 




30 


200,000 


30 to 50 




250,000 
300,000 



















Mr. Kuichling deduces the following formulas for y by the use 
of the preceding tables, i.e., these formulge express the results 
given in the preceding table as nearly as simple forms of formulae 
permit. 

( y min. =i.j^/x + o.o^x, ) 



For Freeman's data : 

For Shedd 's data: 
For Fanning' s data : 
For the author's data : 



y max. =— + 10. 



= \^ ^X = 2.24\^X. 



X 



= 2.8V^ 



(I) 

(2) 
(3) 
(4) 



While for the average ordinary consumption of water, expressed 
in gallons per head and day, q, Mr. Coffin's formula, as given in 
his paper previously cited, may be taken 



q = 4ox°-''^. 



(5) 



By combining equation (5) with equation (4), remembering 
that the maximum rate of consumption is usually about 1.5 
times the average, the total draft in gallons per minute upon 



SUPPLY OF FIRE-STREAMS. 195 

the discharging system at the time of a conflagration will become 
as follows : 

^ , ^ /— s ^40X1000 

■^ ^ ^ ^2 1440 

= 25o(^2.8Vx + ^J. (6) 

This maximum rate of consumption during a conflagration does 
not affect the total supply of a large city like New York, Boston, 
or Chicago, but it may become of relatively great importance in 
a small city or town. In a large city this draft may and fre- 
quently does tax the capacity of a small district of the discharg- 
ing system. In designing such systems, therefore, even for 
large cities, it is necessary to insure all districts against a small 
local supply when a large one may pressingly be needed. 



CHAPTER XV.. 

155. Waste of Water, Particularly in the City of New York. — 

The quantity of water involved in designing a water-supply for 
cities and towns is much larger than that which is actually needed. 
The experience of civil engineers in many cities, both in this 
country and in Europe, shows conclusively that the portion of 
water actually wasted or running away without serving any 
purpose will usually run from 30 to 50 per cent of the total amount 
brought to the distributing system. In the city of New York 
there is strong reason to believe that the wastage is not less than 
two thirds of the total quantity supplied. It is frequently 
assumed that both the quantities supplied and the quantities, 
uselessly wasted in New York are larger than in other places. 
As a matter of fact those quantities are actually smaller than 
in some other large cities. While the supply per inhabitant 
in New York City is much larger than should be required, the 
use of water by its citizens is not extravagant when gauged by 
the criterion of use in other large cities. This question was 
most carefully and exhaustively investigated in 1899 and the 
early part of 1900 by Mr. John R, Freeman of Boston, acting 
for the comptroller of the city of New York. 

The usual wastes of a water-supply system may be dis- 
tributed under six principal heads. First, leaky house-plumb- 
ing; second, and "possibly first in order of magnitude," leaky 
service-pipes connecting the house pipe system with street-mains ; 
third, leaving water-cocks open unnecessarily; fourth, leaky 
joints in street-mains or pipes ; fifth, possibly pervious beds and 
banks of distributing-reservoirs; sixth, stealing or "unlawful 
diversion" of water through surreptitious connections. 

The sixth item is probably an extremely small one in New" 

198 



DIVISION OF DAILY CONSUMPTION IN NEW YORK CITY. 197 

York, although instances of that kind of waste have been found. 
It is an old wastage known as far back in time as the ancient 
Roman water-supply. The second and third items probably 
constitute the bulk of the wastage in this city. 

156. Division of Daily Consumption in the City of New York. — 
In the course of his search for the various sources of consump- 
tion, Mr. Freeman concluded from his examinations and from 
the use of the various means placed at his command for measur- 
ing the daily consumption between December 2d and December 
5th, 1899, and December 8th and December 15th, 1899, that the 
average daily consumption could be divided as follows: 

Gallons per Inhabitant 
per Day. 

Probable average amount really used. ... 40 

Assumed incurable waste io| 

Curable waste, probably-. 65 | '^ 

Daily uniform rate of delivery by 
Croton Aqueduct 115 

In his investigations Mr. Freeman had the elevation of water 
in the Central Park reservoir carefully observed every six min- 
utes throughout the twenty-four hours. At the same time the 
uniform flow through the new Croton Aqueduct was known as 
accurately as the flow through such a conduit can be gauged at 
the present time. Knowing, therefore, the concurrent variation 
of volume in the Central Park reservoir supplied by the new 
Croton Aqueduct and the rate of flow in that aqueduct, the con- 
sumption of water per twenty-four hours would be known with 
the same degree of accuracy with which the flow in the aqueduct 
is measured. It was found by these means that the actual con- 
sumption between the hours of 2 and 4 a.m. was at the rate of 
94 gallons per inhabitant per day, although the actual use at 
that time was as near zero as it is possible to approach during 
the whole twenty -four hours. Nearly all of that rate of con- 
sumption represents waste. 

Summing up the whole matter in the light of his investiga- 
tions, Mr. Freeman made the following as his nearest estimate 



198 WATER-WORKS FOR CITIES AND TOWNS. 

to the actual consumption of the daily supply of water of New 
York City: 

Gallons per In- 
ACTUAL use: habitant per Day. 

Domestic (average) 12 -20 

Manufacturing and commercial 20 —30 

City buildings, etc 2 -4 

Fires, street fltishing and siDrinkling 0,4- o . 7 

Total 34 -55 

Incurable waste (probabilities) : 

Leaks in mains i- 2 

Leaks in old and abandoned service-pipes 1-2 

Poor plumbing, all taps metered and closely inspected 2-3 

Careless and wilful wastes 1-2 

Under-registry of meters i- i 

Total incurable waste and under-registry 6-10 

Minimum use and waste 40-65 

Needless waste: 

Leaks in street-mains (a guess) 15-10 

Leaks in service-pipes between houses and street-mains (a guess) 15-10 

Defective plumbing (a guess) 25-15 

Careless and wilful opening of cocks (a guess) 17-14 

To prevent freezing in winter and for cooling in summer 3-1 

Total needless waste 75-50 

Total consumption 115-115 

157. Daily Domestic Consumption. — The quantity assigned 
in the preceding statement to domestic use is confirmed by the 
abundant experience in other cities where services are carefully 
metered, as in Fall River, Lawrence, and Worcester, Mass., and 
in Woonsocket, R. I., where measurements by meters show that 
the domestic consumption has varied from 1 1 . 2 to 16.3 gallons 
per inhabitant per day. Furthermore, annual reports of the 
former Department of Public Works and the present Depart- 
ment of Water-supply for the City of New York show that during 
the years 1890 to 1898 such meters as have been used in the 
territory supplied by the Croton and the Bronx aqueducts 
indicate a daily consumption varying from 13.8 to 24.2 gallons 
per inhabitant per day. The same character of confirmatory 
evidence can be applied to the quantities assigned to manufac- 
turing and commercial uses, city buildings and fires, street 
flushing and sprinkling. 



INCURABLE AND CURABLE WASTES. 199 

158. Incurable and Curable Wastes. — The items composing 
incurable waste, unfortunately, cannot be so definitely treated. 
It is perfectly well known, however, among civil engineers, that 
a large amount of leakage takes place from corporation cocks, 
which are those inserted in the street-mains to form the connec- 
tion between the latter and the house service-pipes. Again, 
many of these service-pipes are abandoned and insufficiently 
closed, or not closed at all, leaving constantly running streams 
whose continuous subsurface discharges escape detection and 
frequently find their way into sewers. Water-pipes which have 
been laid many years frequently become so deeply corroded as 
to afford many leaks and sometimes cracks. Doubtless there are 
many portions of a great distributing system, like that in New 
York City, which need replacing and afford many large leaks, but 
undiscoverable from the surface. Many lead joints of street- 
mains also become leaky with age, while others are leaky when 
first laid in spite of inspection during construction. Just how 
much these items of waste would aggregate it is impossible accu- 
rately to state, but from careful observations made in other places 
5 to 10 gallons per day per head of population seems reasonable. 
A three-year-old cast-iron fire-protection pipe 5.57 miles long 
and mainly 16 inches in diameter, under an average pressure of 
114 pounds per square inch, was tested in Providence in 1900 and 
showed a leakage at lead joints only of 446 gallons per mile per 
twenty-four hours, which was equivalent to .22 gallon per foot 
of lead joint per twenty -four hours. Further tests in 1900 of 
seven lines of new pipe laid by the Metropolitan Board of Boston, 
and tested under pressures varying from 50 to 150 pounds per 
square inch by Mr. F. P. Stearns, chief engineer, and Mr. Dexter 
Brackett, engineer of Distribution Department, and having an 
aggregate length of 51.4 miles with diameters ranging from 16 
to 48 inches, gave an average leakage per lineal foot of pipe in 
gallons per twenty -four hours ranging from .6 to 3.7 gallons 
(average 2.47 gallons), equivalent to an average leakage of 3 
gallons per twenty-four hours per lineal foot of lead joint. The 
possible rates of leakage from street-mains are to be applied to 
a total length of pipe-lines of 833 miles for the boroughs of Man- 
hattan and the Bronx. The borough of Brooklyn has somewhat 



200 . WATER-WORKS FOR CITIES AND TOWNS. 

over 600 miles of street-mains, but they are not to be considered 
in connection with the Croton and Bronx water-supply. 

All these considerations either confirm or make reasonable 
the estimates of the various items of actual use and waste set 
forth by Mr. Freeman. 

159. Needless and Incurable Waste in City of New York.— 
Concisely summing up his conclusions, it may be stated that in the 
year 1899 the average consumption per inhabitant of the boroughs 
of Manhattan and the Bronx was 115 gallons ; of these 115 gallons 
the needless average waste may be 65 gallons, while the incur- 
able or necessary waste may probably be taken at 10 gallons per 
inhabitant per day. It is further probable that the total under- 
ground leakage in New York City is to be placed somewhere 
between 20 to 35 gallons per inhabitant per day. 

160. Increase in Population. — The total volume of daily 
supply to any community is determined by the population ; but 
the population is as a whole constantly increasing. It becomes 
necessary, therefore, to estimate the capacity of a water-supply 
system in view of the future population of the city to be supplied. 
No definite rule can be set as to the future period for which the 
capacity of any desired system is to be estimated. It may be 
stated that no shorter period of time than probably ten years 
should be considered, indeed it is frequently prudent to provide 
for a period of not less than twenty years, and it may sometimes 
be necessary or advisable to consider a possible source of supply 
for even fifty years. Provision must be made not only for the 
present population, but for the increase during those periods of 
time, or at least for the possible development that may be needed. 

The increase in population of cities will obviously vary for 
different locations with the character of the occupations followed 
and with the development of such important factors of industrial 
life as railroad connections, facilities for marine commerce, the 
capacity for development of the surrounding country, and other 
influences which aid in the increase of commerce and industrial 
activity and the growth of population. It has been observed, 
as a matter of experience, that large cities generally reach a point 
where their subsequent increase of population is represented by 
a practically constant percentage, the value of that percentage 



INCREASE IN POPULATION. 



201 



depending upon local considerations. In 1 893, when it was desired 
to estimate the future population of London for as much as forty 
years, it was found that the increase for the ten years from 1881 
to 1 89 1 was 18.2 per cent, with an average of about 20 per cent 
for several previous decades. It could, therefore, be reasonably 
estimated for the city of London that its population at the end 
of any ten-year period w^ould be 18.2 per cent greater than its 
population at the beginning of that period. In Appendix i of 
the report of the Massachusetts State Board of Health upon the 
Metropolitan water-supply for the city of Boston made in 1895, 
the increases for the two ten-year periods 18 70-1 880 and 1880- 
1890 were 6 per cent and 9.6 per cent respectively for the city 
proper, but for the population within a ten-mile radius from the 
centre of the city they were 28.7 per cent and 33.7 per cent re- 
spectively. The corresponding percentages for the cities of 
New York, Philadelphia, and 'Chicago for the same periods are 
as shown in the following tabular statement : 





Population. 


Percentages of Increase. 




1S70. 


1880. 


1890. 


1870-80. 1880-90. 


New York 

Philadelphia 

Chicago 


1,626,119 
726,247 
310,996 


2. 131. 051 
921,458 
550,618 


2,821,802 
1.162,577 
1,075.158 


31 

27, 

77 


32 
26 

95* 



* Includes added territory. 

Obviously every estimate of this kind must be made upon the 
merits of the case under consideration. The probable increase 
of population for any particular city is sometimes estimated by 
considering the circumstances of growth of some other city of 
practically the same size, and if possible with the same commercial 
industries or residential environment, or making suitable allow- 
ances for variations in these respects. Since it is imperative to 
secure as accurate estimates as practicable, both methods or 
other suitable methods should be employed, in order that the 
results may be confirmed or modified by comparison. In every 
case the supply system should be designed to meet reasonable 
estimated requirements for the longest practicable future period, 
preferably not less than tw^enty years. 



202 WATER-WORKS FOR CITIES AND TOWNS. 

i6i. Sources of Public Water-supplies. — One of the most im- 
portant features of a proposed water-supply is its source, since 
not only the potable qualities are largely affected by it, but fre- 
quently the amount also. The two general classes into which 
potable waters are divided in respect to their sources are surface- 
waters and ground -waters. Surface-waters include rain-water 
collected as if falls, water from rivers or smaller streams, and 
water from natural lakes; they are collected in reservoirs and 
lakes or impounding reservoirs. Ground- waters are those col- 
lected from springs, from ordinary or shallow wells, from deep or 
artesian wells, and from horizontal galleries, hke those some- 
times constructed near and parallel to subsurface streams or in 
subsurface bodies of water, affording opportunity for filtration 
from the latter through sand or other open materials to them. 

The quality of water will obviously be affected by the kind 
of material through which it percolates or flows. Surface- 
waters, flowing over the surface of the ground or percolating but 
a short distance below the surface, naturally have contact with 
vegetable matter, unless they are collected in a country where 
the soil is sandy and where the vegetation is scarce. If such 
waters flow through swamps or over beds of peat or other similar 
vegetable mould or soil, they may become so impregnated with 
organic matter or so deeply colored by it that they are not avail- 
able for potable purposes. Ground-waters, on the other hand, 
possess the advantage of having flowed through comparatively 
great depths of sand or other earthy material essentially free of 
organic matter. They may, however, in some locations, carry 
prejudicial amounts of objectionable salts in solution, rendering 
them unfit for use. As a rule, ground-waters are apt to be of 
better quality than surface-waters, but they do not generally 
stand storage in reservoirs as well as surface potable waters. It 
is advisable to store them in covered reservoirs from which the 
light is excluded, rather than in open reservoirs. They are some- 
times impregnated with salts of iron to such an extent as to make 
it necessary to resort to suitable processes for their removal, and 
they are also occasionally found so hard as to require the employ- 
ment of methods of softening them. 

Both sources of supply are much used in the United States. 



SOURCES OF PUBLIC WATER-SUPPLIES. 203 

Table IV shows the percentages of the various classes of supplies 
as found in this country during the year 1897 ; the total number 
of supplies having been at that time nearly 4000. 

TABLE IV. 

WATER-SUPPLIES OF THE UNITED STATES. 

Source. Per Cent of Total. 

( Rivers 2% 

Surface- , Lakes y 

waters : '] Impounding reservoirs 6 

L Combinations r 



Ground- 
waters : 



Shallow wells 26 

Artesian wells 10 

Springs 15 

Galleries and tunnels i 

Combinations 2 



-38.5 



54 



Surface- and 1 Rivers and ground- waters 6 

ground- - Lakes and ground- waters i 

waters : ( Impounding- reservoirs and ground- waters . t; 



7-5 



Total . 



It will be observed that a little more than one half of the 
suppHes are from ground-waters. The practice in connection 
with European public water-supplies is different in that a con- 
siderably larger percentage of the total is taken from ground- 
waters. 

The original source of essentially all the water available for 
public water-supplies is the rainfall. It becomes of the greatest 
necessity, therefore, to secure all possible information regarding 
rainfall wherever it may be necessary to construct a public water- 
supply. Civil engineers and other observers have for many 
years maintained continuous records of rainfall observations at 
various points throughout the country, but it is within only a 
comparatively short time that the number of those points has 
been large. Through the extension of the work of the Weather 
Bureau, points of rainfall observation are now scattered quite 
generally throughout all States of the Union. The oldest obser- 
vations are naturally found in connection with stations located 
in the Eastern States, where the rainfall is more uniformly dis- 
tributed than in many other portions of the country. Obviously 



204 



WATER-WORKS FOR CITIES AND TOWNS. 



rainfall records become of the greatest importance in those local- 
ities like the semiarid regions of the far West where long periods 
of no rain occur. 

162. Rain-gauges and their Records. — The instrument used 
for the collection of rain in order to determine the amount fall- 
ing in a given time is the rain-gauge, which may be fitted with 
such appliances as to give a continuous record of the rate of 
rainfall. It has been found that the location of the rain-gauge 




Ordinary Rain-gauge. 



has a very important influence upon the amount of rain which 
it collects. It should be placed where wind currents around 
high structures in its vicinity cannot affect its record. The top 
of a large flat-roofed building is a good location in a city, although 
the elevation above the surface of the ground, as is well known, 
affects the quantity of water collected by the gauge. The col- 
lection will be greater at a low elevation than at a high one, in 
consequence of the greater wind currents at the higher point, 
it being well known that less rain will be collected where there is 
the most wind, other things being equal. 

163. Elements of Annual and Monthly Rainfall. — In conse- 
quence of the great variations in the rate of rainfall, not only for 
different portions of the country, but at different times during 
the same storm, it becomes necessary to determine various quan- 
tities such as the maximum, minimum, and mean annual rainfall, 
the actual monthly rainfall for different months of the year, and 



ELEMENTS OF ANNUAL AND MONTHLY RAINFALL. 



205 



the maximum and minimum monthly rainfah for as long a period 
as possible. The minimum monthly rainfall and the minimum 
annual rainfall are of special importance in connection with public 
water-supply and water-power questions, since those minima will, 
in connection with the area of a given watershed, determine the 
srreatest amount of water which can be made available for use. 





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DEC. 


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MONTHLY VARIATIONS IN RAINFALL. 



Fig. I. 



In entering upon the consideration of such questions, therefore, 
civil engineers must inform themselves with the greatest detail 
as to the characteristics of the monthly and the annual rainfall 
of the locality in which their works are to be located. 

The diagram Fig. i and Table V are constructed from data 
given in the bulletins of the Weather Bureau and exhibit some 



206 



WATER-WORKS FOR CITIES AND TOWNS. 



TABLE V. 
GENERAL RAINFALL STATISTICS FOR THE UNITED STATES. 



Station. 





Per Cent 




of 


Mean 


Summer 


Yearly- 


and 


Rainfall. 


Autumn 




Rain to 




Mean 




Yearly. 


45-4 


50 


44-7 


52 


42.3 


52 


42.9 


51 


53-7 


61 


49.1 


61 


48.0 


50 


54-1 


65 


38.2 


70 


52.5 


42 


62.6 


51 ■ 


60.3 


52 


47-7 


58 


50.2 


46 


36.6 


53 


42.1 


50 


42 . 2 


51 


42 . 6 


47 


47.2 


48 


32.5 


56 


36.6 


54 


30.7 


63 


40.8 


52 


34 -o 


54 


31.0 


55 


33-2 


58 


28.2 


63 


31-4 


63 


18. 1 


61 


14-3 


48 


12 . 7 


55 


II. 7 


65 


14 .6 


69 


18.8 


39 


15-4 


38 


77.0 


33 


46 . 2 


31 


19.9 


16 


23-4 


17 


17.2 


15 


9 7 


18 



Per Cent 
Driest 

Year to 
Mean 
Year. 



Per Cent 


Per Cent 


Two 


Three 


Driest 


Driest 


Years. 


Years. 


70 


80 


77 


80 


75 


80 


71 


74 


80 


81 


55 


62 


88 


87 


77 


83 


61 


73 


80 


83 


75 


78 


75 


77 


65 


72 


73 


83 


78 


85 


72 


71 


76 


82 


75 


81 


81 


85 


72 


79 


74 


81 


81 


. 88 


65 


75 


80 


86 


74 


73 


58 


68 


54 


75 


63 


70 


67 


72 


71 


77 


62 


75 


79 


80 


63 


66 


64 


74 


81 


86 


68 


77 


76 


79 


67 


84 


73 


78 


48 


59 


54 


61 



North Atlantic : 

Boston 

New York 

Philadelphia 

Washington 

South Atlantic : 

Wilmington 

Charleston 

Augusta 

Jacksonville 

Key West 

Gulf and Lower Mississippi 

Montgomery 

Mobile ' 

New Orleans 

Galveston 

Nashville 

Ohio Valley: 

Pittsburg 

Cincinnati 

Indianapolis 

Cairo 

Louisville 

Lake Region: 

Detroit 

Cleveland 

Duluth 

Upper Mississippi Valle}' : 

St. Louis. 

Chicago 

Milwaukee 

Madison 

St. Paul 

The Plains: 

Omaha 

North Platte 

Denver 

Cheyenne 

The Plateau: 

Tucson 

Santa Fe 

Salt Lake City 

Walla Walla 

Pacific Coast: 

Astoria 

Portland 

Sacramento 

San Francisco 

Los Angeles 

San Diego 



60 
62 
70 
69 

75 
48 
81 
74 
54 

76 
68 
64 

50 
67 

70 
60 

59 
62 

74 

65 
71 
65 

55 
66 
66 
39 

53 

57 
56 
59 
39 

44 
53 
55 
46 

64 
67 

42 
51 
33 
30 



HOURLY OR LESS RATES OF RAINFALL. 207 

of the general features of the rainfall for different points through- 
out this country. The heavy lines of the diagram show the 
average monthly precipitation at the points indicated, for periods 
of a considerable number of years, as shown in the table. It 
will be observed that the rainfall is comparatively uniform in the 
North Atlantic States but quite variable on the Pacific coast, 
as well as in the Mississippi and Missouri valleys and west of 
those valleys. 

164. Hourly or Less Rates of Rainfall. — Although not often of 
great importance in connection with public water-supply systems, 
it is sometimes necessary to possess data regarding maximum 
hourly (or less) rates of precipitation in connection with sewer 
or drainage work. The earlier records give exaggerated reports 
of maximum rates of rainfall, although that rate varies rapidly 
with the time. Throughout a rain-storm the rate of precipitation 
is constantly varying and th'e maximum rate seldom if ever 
extends over a period equal to a half-hour ; usually it lasts but a 
few minutes only. In this country an average rate of i inch per 
hour, extending throughout one hour, is phenomenal, although 
that rare amount is sometimes exceeded. A maximum rate of 
about 4 inches per hour, lasting 15 to 30 minutes, is, roughly 
speaking, about as high as any precipitation of which we have 
reliable records. The waste ways or other provisions for the 
discharge of surplus or flood waters of the Metropolitan Water- 
supply of Boston are designed to afford rehef for a total pre- 
cipitation of 6 inches in twenty -four hours. It is safe to state 
that an excess of that accommodation will probably never be 
required. 

165. Extent of Heavy Rain-storms.— In all engineering ques- 
tions necessitating the consideration of these great rain-storms 
it is necessary to remember that their extent is frequently much 
greater than the areas of watersheds usually contemplated m 
connection with water-supply work. The late Mr. James B. 
Francis found in the great storm of October, 1869, which had 
its maximum intensity in Connecticut, that the area over 
which 6 inches or more of rain fell exceeded 24,000 square 
miles, and that the area over which a depth of 10 inches or more 
fell was 5 1 9 miles. Again, in the New England storm of February, 



208 



WATER-WORKS FOR CITIES AND TOWNS. 



1886, 6 inches or more of rain fell over an area of at least 3000 
square miles. Storm records show that as much as 8 or 10 inches 
in depth have fallen over areas ranging from 1800 to 500 square 
miles, respectively, in a single storm. 

166. Provision for Low Rainfall Years. — The capacity of any 
public water-supply must evidently be sufficient to meet not 
only the general exigencies of the year of lowest rainfall, but 
also the conditions resulting from the driest periods of that 
year. It is customary among civil engineers to consider 
months as the smaller units of a dry year. It is necessary, there- 
fore, to examine not only the annual rainfalls but the monthly 
rates of precipitation during critical years, i.e., usually during 
dry years. 

It is impossible to determine absolutely the year of least rain- 
fall which may be expected, but evidently the longer the period 
over which observations have extended the nearer that end will 
be attained. It is sometimes assumed that the lowest annual 
rainfall likely to be expected in a long period of years is 80 per 
cent of the average annual rainfall for the same period. Or, it 
is sometimes assumed that the average rainfall for the lowest 
two or three consecutive years will be 80 per cent of the average 
for the entire period, and that the year of minimum rainfall may 
be expected to yield two thirds of the annual average precipi- 
tation. Such features will necessarily vary with the location 

TABLE VI. 



January. . . 
February. . 
March. . '. . . 

April 

May , 

June 

July 

August... . , 
September, 
October. . , 
November 
December. 



Mean 
Monthly 
Rainfall, 
Inches. 



Respective 
Ratios. 



Probable 
Depth in 
Inches of 
Actual 
Rainfall. 



X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 
X 



65 

50 

65 

45 

85 

75 
35 
25 
30 
45 
20 
60 



= 6.6 

= 6.0 

= 6.6 

= 5-8 
3-4 

= 3-0 

= 1.4 

= 1 .0 

= 1.2 

= 1.8 

= 4.8 

= 6.4 



AVAILABLE PORTION OF RAINFALL 209 

of the district considered. Conclusions which may be true for 
the New England or northern Atlantic States probably will not 
hold for the south Atlantic and Gulf States. Data for such 
conclusions must be obtained from the rainfall of the locality 
considered. Table VI exhibits the comparative monthly rain- 
fall which J. T. Fanning suggests may be used approximately 
for the average Atlantic coast districts. 

If the average monthly rainfall throughout the year were one 
inch, the values of the ratios would show the actual monthly 
precipitation. In general the table would be used by dividing 
the total yearly rainfall by 1 2 , and then multiplying that monthly 
average by the proper ratio taken from the table opposite the 
month required. Such tables should only be used for approx- 
imate purposes and when actual rainfall records are not available 
for the district considered. 

167. Available Portion of Rainfall or Run-off of Watersheds. 
■ — If the public water-supply is to be drawn from a stream where 
the desired rainfall records exist, it is necessary to know what 
portion of the rainfall, either in the driest or in other years, may 
be available. This is one of the departments of the hydraulics 
of streams for which much data yet remain to be secured. The 
watersheds or areas drained by some streams, like the Sudbury 
River of the Boston, and the Croton of the New York water- 
supply, have, however, been studied with sufficient 'care to give 
reliable data. The amount of water flowing in a stream from 
any watershed for a given period, as a year, is called the annual- 
"run-off" of the watershed, and it is usually expressed as a 
certain percentage of the total rainfall on the area drained. 
For certain purposes it is sometimes more convenient to express 
the run-off from the watershed as the number of cubic feet of 
water per second per square mile of area. Table VII, taken 
from Turneaure and Russell, exhibits run-off data for a consider- 
able number of streams in connection with both average and 
minimum rainfalls. 

The information to be drawn from this table is sufficient to 
give clear and general relations between the recorded precipita- 
tion and run-off. The percentage of run-off is seen to vary quite 
widely, but as a rule it is materially less for the year of minimum 



210 



WATER-WORKS FOR CITIES AND TOWNS. 



TABLE VII. 
STATISTICS OF THE FLOW OF STREAMS. 



Stream. 



Area 

Drained, 

Square 

Miles. 



Years. 



Average Yearly. 



Rain, 
Inches 



Flow, 
Inches. 



Per 
Cent. 



Year of Minimum 
Flow. 



Rain, 
Inches. 



Flow, 
Inches. 



Per 

Cent. 



Sudbury 

Cochituate 

Mystic 

Connecticut 

Croton 

Upper Hudson. . . 

Genesee 

Passaic. . . 

Upper Mississippi 



75-2 
18.8; 
26 .9 
10,234 
338 

4,500 

1,060 

822 

3,265 



1875-97 
1863-96 
1878-96 
1871-85 
1870—94 
1888-96 
1894-96 
1877-93 
1885-99 



22,22 

20.33 
19.96 

25-25 
24-57 
23-36 
12.95 
25-44 
4-90 



48.6 
43-2 
45-6 

56.5 
50.8 

59-0 

32.5 
54-0 
18.4 



32.78 
31 .20 
31 .22 
40 . 02 
38.52 
33-49 
31 .00 

35-64 
22 .86 



II . 19 
9.76 
9-32 

18.25 

14-54 

17.46 

6.67 

15-23 
1 . 62 



34-1 
31-3 
29.8 

45-6 
37-8 

52.2 

21-5 
42.7 

7-1 



Stream. 



Area 

Drained, 

Square 

Miles. 



Average for December 
to May. 



Years. 



Rain, 
Inches. 



Flow, 
Inches. 



Per 

Cent. 



Average for June to 
November. 



Rain, 
Inches 



Flow, 
Inches. 



Per 

Cent. 



Sudbury 

Cochituate. . . , 

Mystic 

Connecticut. . 

Croton 

Upper Hudson 

Genesee 

Passaic 



75 

18, 

26 

10,234 

338 

4,500 

1 ,060 

822 



1875-97 
1863-96 
1878-96 
1871-85 
1870—94 
1888-96 
1894—96 
1877-93 



22 . 98 
22.97 
22.11 
20.13 

23-39 
18.20 

19.58 
22.47 



17-52 
14-87 
15.12 

17-95 
17.81 
16.23 
10 . 20 
18.22 



76 .0 

64.7 
68.4 
89.1 
76. 1 
89.0 
52.2 
81. 1 



22 .61 
24. 10 
21 .66 
24.56 
24.99 
21.50 
20 . 24 
2439 



70 


20 


46 


22 


84 


22 


30 


29 


76 


27 


13 


33 


75 


13 


19 


29 



flow than for the average year. That feature of the table is an 
expression of the general law, other things being equal, that the 
smaller the precipitation the less will be the percentage of run-off. 
A number of influences act to produce that result. During a 
year of great precipitation the earth is more nearly saturated 
the greater part of the time, and hence when rain falls less of it 
will percolate into the ground and more of it will run off. Again, 
if the ground is absolutely dry, a certain amount of rain would 
have to fall before any run-off would take place. The area and 
shape of a watershed will also affect to some extent the flow of 
the stream which drains it. A larger run-off would reasonably be 
expected from a long narrow watershed than from one more 
nearly circular in outline. The greater the massing of the water- 



RUN-OFF OF SUDBURY WATERSHED. 



211 



shed, so to speak, the more opportunity there is for the water 
to be held by the ground and the less would be the run-off. 

TABLE VIII. 

AVERAGE YIELD OF SUDBURY WATERSHED, 1875-1899, INCLUSIVE, 
VARIOUSLY EXPRESSED. 

(Area of watershed, 75.2 square miles.) 



Month. 



A Square Mile. 



Cubic Feet 
per Second. 



Million 
Gallons 
per Day. 



Rainfall. 



Collected, 
Inches. 



Per Cent 
Collected. 



Total, 
Inches. 



January. . 
February. , 
March. . . . 

April 

May 

June 

July 

August. . . . 
September, 
October. . . 
November. 
December. 

Year. 



I 


937 


1.252 


2 


233 


51.6 


4- 


2 


904 


1.877 


3 


050 


71.7 


4- 


4 


489 


2 .901 


5 


175 


117 .4 


4- 


^ 


124 


2.019 


3 


485 


107-5 


3- 


I 


680 


1.086 


I 


936 


58.1 


3- 




735 


■475 




821 


28.0 


2 . 




305 


.197 




352 


9-3 


3- 




478- 


■309 




551 


^3-3 


4- 




376 


• 243 




419 


13.0 


3- 




829 


•536 




956 


21.9 


4- 


I 


474 


■953 


I 


<^4S 


39-0 


4- 


I .612 


I .042 


1.859 


51-9 


3- 


I 


655 


1 .070 


22 


482 


49.1 


45 



168. Run-off of Sudbury Watershed. — Table VIII has been 
given by Mr. Charles W. Sherman, as representing the average 
yield of the Sudbury watershed for the period 1875 to 1899, 
inclusive, expressed in several different ways. The average 
rainfall was 45.83 inches, and the percentage which represents 
the run-off is 49.1 per cent of the total. The average monthly 
run-off varies from .305 cubic foot (for July) to 4.489 cubic feet 
(for March) per second per square mile. As a general rule it 
may be stated that the average run-off from the drainage areas 
of New England streams amounts very closely to 1,000,000 gal- 
lons per square mile per day. The area of the Sudbury water- 
shed is 75.2 square miles, with 6.5 per cent of that total area 
occupied by the surface of lakes or reservoirs. As will presently 
be seen, the amount of exposed water surface in any watershed 
has an appreciable influence upon its run-off. 

169. Run-off of Croton Watershed. — The total area of the 
Croton watershed, from which New York City draws its supply, 



212 



WATER-WORKS FOR CITIES AND TOWNS. 



i.e., the area up-stream from the new Croton Dam, is 360.4 
square miles, of which 16. i square miles, or 4.47 per cent, of its 
total area is water surface. Mr. John R. Freeman found in the 
investigations covered by his report to the comptroller of the city 
of New York in 1900 that the average annual rainfall on that 
area for the thirty- two years beginning 1868 and ending 1899 
was 48.07 inches, and that the average run-off for the same 
period was 47.7 per cent of the total average rainfall, equivalent 
to a depth of 22.93 inches. 




Aqueducts near Jerome Park Reservoir, New York City. 



Table IX gives the main elements of the rainfall and run-off 
for the Croton watershed during the thirty-two year period, for 
the averages just given. 

The table shows that the least annual rainfall was 36.92 
inches for 1880, and that the run-off represented a depth of 12.63 
inches only, or 34.21 per cent of the total annual precipitation. 



EVAPORATION FROM RESERVOIRS. 



213 



TABLE IX. 

RAINFALL ON CROTON WATERSHED IN TOTAL INCHES— 1868-1898. NATURAL 
FLOW OF CROTON RIVER AT OLD CROTON DAM, IN EQUIVALENT INCHES 
PERCENTAGE OF RUN-OFF TO RAINFALL FOR EACH YEAR. 



Year. 


Total 
Rainfall. 


Total 
Run-off. 


Per Cent. 


Year. 


Total 
Rainfall. 


Total 
Run-off. 


Per Cent. 


1868 


50.33 


33-33 


66 '. 22 


1885 


43-67 


17.71 


40.55 


1869 


48.36 


23.61 


48.82 


1886 


47 


-74 


20. 10 


42 


10 


1870 


44 63 


19. 20 


43.02 


1887 


57 


29 


26.61 


46 


45 


1871 


48.94 


19.46 


3976 


1888 


60 


69 


35-27 


58 


12 


1872 


40.74 


16.92 


41-53 


1889 


55 


70 


31-39 


56 


36 


1873 


43-87 


25 . 02 


57-03 


1890 


54 


05 


25-95 


48 


01 


1S74 


42.37 


25.10 


59-24 


1891 


47 


20 


23.48 


49 


75 


1875 


43.66 


24.77 


56.73 


1892 


44 


28 


17.68 


39 


93 


1876 


40.68 


21 .09 


51.84 


1893 


54 


87 


29.05 


52 


94 


1877 


48.23 


20 . 22 


41 .92 


1894 


47 


33 


20.56 


43 


44 


1878 


55-70 


27.17 


48.78 


1895 


40 


58 


15.95 


39 


31 


1879 


47.04 


19.65 


41.77 


1896 


45 


85 


23.26 


50 


73 


1880 


36.92 


12.63 


34-21 


1897 


53 


12 


25.59 


48 


17 


1881 


46 .69 


19-25 


41 -23 


1898 


57 


40 


29.72 


51 


77 


1882 


52.35 


24.28 


46.38 


1899 


44 


67 


22 . 28 


49 


88 


1883 
1884 


42.70 
51.28 


^3-33 
24 . 08 


31 .22, 
46 .96 


Average for 
32 years. 


48 


07 


22.93 


47 


70 



As a rule the same feature of a lov^ percentage of run-off will be 
found belonging to the years of lov^ rainfall, although there are 
many irregularities in the results. On the other hand, the high 
percentages of run-off are for the years 1868, 1888, and 1889, and 
they v^ill generally be found belonging to years of relatively great 
precipitation. A low percentage of run-off will also, be lower if 
the year to which it belongs follows a dry year or a dry cycle of 
two or three years. Similarly the high percentages of run-off 
will, as a rule, be higher if they follow years of high precipitation ; 
that is, if they belong to a cycle of relatively great rainfall. 

170. Evaporation from Reservoirs. — If it is contemplated to 
build reservoirs on a watershed the capacity of which is being 
estimated on the basis of either the driest year or the driest two- 
or three-year cycle, it is necessary to make a deduction from the 
rainfall for the evaporation which will take place from the sur- 
face of the proposed reservoir. In order that that deduction may 
be made as a proper allowance for added water surface in a drain- 
age area, it is necessary that the amount of evaporation be deter- 
mined for the district considered. The rate of evaporation is 
dependent upon the area of water surface, upon the wind, and upon 
the temperature both of the water and air above it. Numerous 



214 



WATER-WORKS FOR CITIES AND TOWNS. 



evaporation observations have been made both in this and other 
countries, and extensive evaporation tables have been prepared 
by the Weather Bureau, from which a reasonable estimate of the 
monthly evaporation for all months in the year may be made for 
almost any point in the United States. Particularly available 




Aqueduct Division Wall of Jerome Park Reservoir, New York City. 



observations have been made by Mr. Desmond Fitzgerald of 
Boston on the Chestnut Hill reservoirs of the Boston Water- 
supply, and by Mr. Emil Kuichling, engineer of the Rochester 
Water-works, on the Mount Hope reservoir of the Rochester- 
supply. Table X exhibits the results of the observations of both 
these civil engineers. 

As would be anticipated, the period from May to September, 
both inclusive, shows by far the greatest evaporation of the 
whole year, while December, January, and February are the 
months of least evaporation. The total annual evaporation 
at Boston was 39.2 inches and 34.54 inches at Rochester. 



EVAPORATION FROM THE EARTH'S SURFACE. 



215 



TABLE X. 
MEAN MONTHLY EVAPORATIONS. 



Month. 



Chestnut Hill Reservoir, 
Boston, Mass. 



Evaporation, 
Inches. 



Per Cent 

of Yearly 

Evaporation. 



Mount Hope Reservoir, 
Rochester, N. Y. 



Evaporation, 


Inches. 


o 


52 


O 


54 


I 


33 


2 


62 


3 


93 


4 


94 


5 


47 


5 


30 


4 


15 


3 


16 


I 


45 


I 


13 



Per Cent 

of Yearly 

Evaporation. 



January 

February 

March 

April 

May 

June 

July 

August 

September 

October 

November 

December 

Total for year 

Mean temperature 



. 96 
1.05 

1 . 70 
2.97 
4.46 
5-54 
5-98 

5-5° 
4.12 
3.16 
2.25 
1-51 



39 -20 



1-5 
1.6 

3-9 

7.6 

II .4 

14-3 
15.8 

15-4 

12.0 

9.1 

4.2 

3-2 



34-54 



48°. 6 



47 



A reference to data of the Weather Bureau will show that 
annual evaporation as high as 100 inches, or even more, may be 
expected on the plateaux of Arizona and New Mexico. Other 
portions of the arid country in the western part of the United 
States will indicate annual evaporations running anywhere from 
50 to go inches per year, while on the north Pacific coast it will 
fall as low as 18 to 40 inches. 

171. Evaporation from the Earth's Surface. — Data are lack- 
ing for anything like a reasonably accurate estimate of evapora- 
tion from the earth's surface. It is well known that the loss of 
water from that source is considerable in soils like those of 
swamps, particularly when exposed to the warm sun, but no 
reliable estimate can be obtained for the exact amount. Nor 
is this necessary for the usual water-supply problems, since it 
is included in the difference between the total rainfall of any 
district and the observed run-off in the streams. Indeed evapo- 
ration from reservoirs is similarly included for reservoirs existing 
when the run-off observations are made. 



CHAPTER XVI. 

172. Application of Fitzgerald's Results to the Croton Water- 
shed. — The evaporation data determined by Messrs. Fitzgerald 
and Kuichling are sufficient for all ordinary purposes in the 
North Atlantic States. In the discussion of the capacity of the 
Croton watershed Mr. Fitzgerald's results will be taken, as the 
conditions of the Croton watershed in respect to temperature 
and atmosphere are affected by the proximity to the ocean, and 
other features of the case make it more nearly like the Metropoli- 
tan drainage area near Boston than the more elevated inland 
district near Rochester. 

If the monthly amounts of evaporation be taken from the 
preceding table, and if it further be observed that a volume of 
water i square mile in area and i inch thick contains 17,377,536 
gallons, the following table (Table XI) of amounts of evapora- 
tion from the reservoirs in the Croton watershed, including the 
new Croton Lake, will result, since the total area of water surface 
of all these reservoirs is 16. i square miles. 



TABLE XI. 



Jan. 

Feb. 

Mar. 

April 

May 

Tune 

July 

Aue. 



0.96X16. I Xi7,377,536 = 



I-05X 
1 .70X 
2.97 X 
4-46X 
5 ■ 54 X 
5-98X 
.S 50X 
Sept. 4.12X 
Oct. 3.16X 
Nov. 2 . 25 X 
Dec. 1 . 51 X 

39.20 



268,600,000 gallons. 

= 293,800,000 

= 475,700,000 

= 831.000,000 

— 1,247,900,000 

= 1,550,100,000 

= 1,673,200.000 

== 1,538,900,000 

= 1,152,800,000 

= 884,200,000 

= 620,600.000 

= 422,^00,000 



Total =10, 



,300,000 



216 



THE CAPACITY OF THE CROTON WATERSHED. 317 

It will be seen from this table that the total annual evaporation 
from all the reservoir surfaces of the Croton watershed, as it will 
exist when the new Croton Lake is completed, will be nearly 
11,000,000,000 gallons, enough to supply the boroughs of Bronx 
and Manhattan at the present rate of consumption for about 
forty days. 

173. The Capacity of the Croton Watershed. — The use of the 
preceding figures and numbers can be well illustrated by con- 
sidering the capacity of the Croton watershed in its relations 
to the present water needs of the boroughs of Bronx and Man- 
hattan which that watershed is designed to supply. The total 
area of the Croton watershed is 360.4 square miles, of which 16. i 
square miles, as has already been observed, is water surface. 
As a matter of fact the run-off observations from that watershed 
have been maintained or computed for the thirty-two-year period 
from 1868 to 1899, inclusive, covering the evaporation from the 
reservoirs and lake surfaces as they have existed during that 
period. The later observations, therefore, include the effects 
of evaporation from the more lately constructed reservoirs, but 
none of these data cover evaporation from the entire surface of 
the new Croton Lake, whose excess over that of the old reservoir 
is nearly one third of the total water surface of the entire shed. 
As a margin of safety and for the purpose of simplification, sepa- 
rate allowance will be made for the evaporation from all the 
reservoir and lake surfaces of the entire watershed as it will exist 
on the completion of the new Croton Lake, as a deduction from 
the run-off. The preceding table (Table XI) exhibits those 
deductions for evaporation as they will be made in the next 
table. 

In Table IX the year 1880 yields the lowest run-off of the 
entire thirty-two-year period. The total precipitation was 36.92 
inches, and only 34.21 per cent of it was available as run-off. 
The first column in Table XII gives the amount of monthly rain- 
fall for the entire year, the sum of which aggregates 36.92 inches. 
Each of these monthly quantities multiplied by .3421 will give 
the amount of rainfall available for run-off, and the latter quan- 
tity multiplied by the number of square miles in the watershed 
(360.4) will show the total depth of available water concentrated 



218 



WATER-WORKS FOR CITIES AND TOWNS. 



(Jan. 3.43 X. 3-1 


21 =1.173) X36 


0.4X 


(Feb. 3.40 X ' 


' =1.163) X ' 


' X 


(Mar. 3.90 X ' 


' =1.334) X ' 


' X 


(April 3.57 X ' 


' =1.221) X ' 


' X 


(May 1.04 X ' 


' = .356) X 


' X 


(June 1.40 X 


' = -479) X ' 


' X 


(July 5.86 X ' 


' =2.005) X 


' X 


(Aug. 4.16 X ' 


' =1.423) X ' 


' X 


(Sept. 2.42 X ' 


' = .828) X ' 


' X 


(Oct. 2.83 X ' 


' = .968) X ' 


' X 


(Nov. 2.32 X 


' = .794) X ' 


' X 


(Dec. 2.59 X 


' = .886) X ' 


' X 



upon a single square mile. If the latter quantity be multiplied 
by 17,378,000, the total number of gallons available for the entire 
month will result, from which must be subtracted the evaporation 
for the same month. Carrying out these operations for each 
month in the year, the monthly available quantities for water- 
supply will be found, as shown in the last column. 

TABLE XII. 
60.4X17,378,000— 268,600,000= 7,077,700,000 

" — 293,800,000 = 6,989,900,000 

" — 475,700,000 = 7,879,000,000 

" — 831,000,000= 6,816,000,000 

" — 1,247,900,000= 982,000,000 

" — 1,550,100,000= 1,449,800,000 

" — 1,673,200,000=10,890,000,000 

" — 1,538,900,000= 7,373,100,000 

" — 1,152,800,000= 4,032,900,000 

" — 884,200,000= 5,178,500,000 

" — 629,600,000= 4,343,100,000 

" . — 422,500,000= 5,126,300,00a 

36.92 

The sum of the twelve monthly available quantities will give 
the total number of gallons per year applicable to meeting the 
water demands of the boroughs of Bronx and Manhattan. 

174. Necessary Storage for New York Supply to Compensate 
for Deficiency. — At the present time the average daily consump- 
tion per inhabitant of those two boroughs is 115 gallons, and if 
the total population be taken at 2,200,000, the total daily con- 
sumption will be 2,200 000X115=253,000,000 gallons. If the 
latter quantity be multiplied by 30.5, the latter being taken as 
the average number of days in the month throughout the year, 
the average monthly draft o f water for the two boroughs in ques- 
tion will be 7,716,500,000 gallons. The subtraction of the latter 
quantity from the monthly results in the preceding table will 
exhibit a deficiency which must be met by storage or a surplus 
available for storage. Table XIII exhibits the twelve monthly 
differences of that character. 

It is seen from this table that the total monthly deficiencies 
aggregate 27,795,700,000 gallons and that there are only two 
months in which the run-off exceeds the consumption, the sur- 
plus for those two months being only 3,336,000,000 gallons. 



NECESSARY STORAGE FOR NEW YORK SUPPLY. 219 

TABLE XIII. 

7,077,700,000—7,716,500,000= — 638,800,000 

6,989,900,000— " = — 726,600,000 

7,879,000,000— " = + 162,500,000 

6,816,000,000 — " = — 900,500,000 

982,000,000 — " = — 6,734,500,000 

1,449,800,000— " = — 6,266,700,000 

10,890,000,000— " = +3,173,500,000 

7,373,100,000— " ■ = — 343,400,000 

4,032,900,000 — " = — 3,683.600,000 

5,178,500,000— " = — 2,538,000,000 

4.343.100,000— ^'^' = — 3,373,400,000 

5,126,300,000 — " = — 2,590,200.000 

— 27,795,700,000 +3,336,000,000 
+ 3,336,000,000 

— 24,459,700,000 

The total deficiency for the year is therefore 24,459,700,000 
gallons. Dividing the latter quantity by the average daily 
draft of 253,000,000 gallons, there will result a period of 97 days, 
or more than one quarter of a year, during which the minimum 
annual rainfall would fail to supply any water to the city at all. 
These results show that in case of a low rainfall year, like that 
of 1880, the precipitation upon the Croton watershed would 
supply sufficient water for the boroughs of Bronx and Manhattan 
at the present rate of consumption for three fourths of the year 
only. A distressingly serious water famine would result unless 
the year were begun by sufficient available storage in the reser- 
voirs of the basin at least equal to 24,459,700,000 gallons. 
Should such a low rainfall year or one nearly approaching it be 
one of a two- or three-year low rainfall cycle, such a reserve 
storage would be impossible and the resulting conditions would 
be most serious for the city. If an average year, for which the 
total rainfall would be about 48 inches preceded such a year of 
low rainfall, the conditions would be less serious. The figures 
would stand as follows : 
Total run-off = 

17-377. 536X360. 4X22. 93 -1 7, 377, 536X16. 1X39 -2 

= 132,640,000,000 gallons. 
Total annual consumption = 92,345,000,000 

Available for storage = 40,295,000,000 

Deficiency = 24,459,700,000 

Surplus = 15,835,300,000 



2'20 WATER-WORKS FOR CITIES AND TOWNS. 

The average year would, therefore, yield enough run-off water 
if stored to more than make up the deficiency of the least rainfall 
year by nearly 16,000,000,000 gallons. In order to secure the 
desired volume it would therefore be necessary to have storage 
capacity at least equal to 24,459,700,000 gallons; indeed, in 
order to meet all the exigencies of a public water-supply it would 
be necessary to have far more than that amount. As a matter 
of fact there are in the Croton watershed seven artificial reser- 
voirs with a total storage capacity of nearly 41,000,000,000 gal- 
lons, besides a number of small ponds in addition to the new 
Croton Lake which with water surface at the masonry crest of 
the dam has a total additional storage capacity of 23,700,000,000 
gallons. The storage capacity of the new Croton Lake may be 
increased by the use of flash-boards 4 feet high placed along its 
crest, so that with its water surface at grade 200 its total capacity 
will be increased to 26,500,000,000 gallons. After the new 
Croton reservoir is in use the total storage capacity of all the 
reservoirs and ponds in the Croton watershed will be raised to 
70,245,000,000 gallons, which can be further augmented by the 
Jerome Park reservoir when completed by an amount equal to 
1,900,000,000 gallons. This is equivalent, at the present rate 
of consumption, to a storage supply for 285 days for the boroughs 
of Manhattan and the Bronx. 

175. No Exact Rule for Storage Capacity. — This question of 
the amount of storage capacity to be provided in connection 
with public water-supplies is one which cannot be reduced to 
an exact rule. Obviously if the continuous flow afforded from 
any source is always greater per day than any draft that can ever 
be made upon it, no storage -reservoirs at all would be needed, 
although they might be necessary for the purpose of sedimenta- 
tion. On the other hand, as in the case of New York City, if the 
demand upon the supply has reached its capacity or exceeded it 
for low rainfall years, it may be necessary to provide storage 
capacity sufficient to collect all the run-off of the watershed. 
The civil engineer must from his experience and from the data 
before him determine what capacity between those limits is to 
be secured. When the question of volume or capacity of storage 
is settled the mode of distribution of that volume or capacity 



THE COLOR OF WATER. 221 

in reservoirs is to be determined, and that affects to some extent 
the potabiUty of the water. If there is a large area of shallow 
storage, the vegetable matter of the soil may affect the water in 
a number of ways. Again, it is advisable in this connection to 
consider certain reservoir effects as to color and contained organic 
matter in general. 

176. The Color of Water. — The potability* of water collected 
from any watershed is materially affected by its color. Although 
iron may produce a brownish tinge, by far the greater amount 
of color is produced by dissolved vegetable matter. Repeated 
examinations of colored water have shown that discoloration is 
in many cases at least a measure of the vegetable matter con- 
tained in it. While this may not indicate that the water is 
materially unwholesome, it shows conclusively the existence 
of conditions which are usually productive of minute lower 
forms of vegetation from which both bad taste and odors are 
likely to arise. 

There are two periods in the year of maximum intensity of 

* What is generally known as the "Michigan standard of the purity of 
drinking-water," as specified by the Michigan State Laboratory of Hygiene, 
is here given: 

"1. The total residue should not exceed 500 parts per million. 

"2. The inorganic residue may constitute the total residue. 

"3. The smaller amount of organic residue the better the water. 

"4. The amount of earthy bases should not exceed 200 parts per million. 

"5. The amount of sodium chloride should not exceed 20 parts per million 
(i.e., 'chlorine' 12.1 parts per million). 

"6. The amount of sulphates should not exceed 100 parts per million. 

"7. The organic matter in 1,000,000 parts of the water' should not reduce 
more than 8 parts of potassium permanganate (i.e., 'required oxygen' 2.2 parts 
per million) . 

"8. The amount of free ammonia should not exceed 0.05 part per million. 

"9. The amount of albuminoid ammonia should not exceed 0.15 part per 
million. 

"10. The amount of nitric acid should not exceed 3.5 parts per miUion 
(i.e., 'N as nitrate' .9 part per million). 

"it. The best water contains no nitrous acid, and any water which con- 
tains this substance in quantity sufficient to be estimated should not be re- 
garded as a safe drinking-water. 

"12. The water must contain no toxicogenic germs as demonstrated by 
tests upon animals. 

"The water must be clear and transparent, free from smell, and without 
either alkaline or acid taste, and not above 5 French standard of hardness." 

This standard is too high to be attained ordinarily in natural waters. 



222 WATER-WORKS FOR CITIES AND TOWNS. 

color, one occurring in June and the other in November. The 
former is due to the abundant drainage of peaty or other exces- 
sively vegetable soils from the spring rains. After June the 
sun bleaches the water to a material extent until the autumn, 
when the dying vegetation imparts more or less coloring to the 
water falling upon it. This last agency produces its maximum 
effect in the month of November. 

There are various arbitrary scales employed by which colors 
may be measured and discolored waters compared. Among 
others, dilute solutions of platinum and cobalt are used, in which 
the relative proportions of those substances are varied so as to 
resemble closely the colors of the water. The amount of plati- 
num used is a measure of the color, one unit of which corresponds 
to one part of the metal in 10,000 parts of water. Again, the 
depth at which a platinum wire i mm. (.039 inch) in diameter 
and I inch long can be seen in the water is also taken as a measure 
of the color, the amount of the latter being inversely as the depth. 
This method has found extended and satisfactory use in connec- 
tion with the Metropolitan Water-supply of Boston, the Cochi- 
tuate water having a degree of color represented by .25 to .30, 
while the Sudbury water has somewhat more than twice as 
much. The Cochituate water is practically colorless. 

The origin of the color of water is chiefly the swamps which 
drain into the water-supply, or the vegetation remaining upon a 
new reservoir site when the surface soil has not been removed 
before the filling of the reservoir. The drainage of swamps 
should not, as a rule, be permitted to flow into a public water- 
supply, as it is naturally heavily charged with vegetable matter 
and is correspondingly discolored. .This matter, hke many others 
connected with the sanitation of potable public waters, has been 
most carefully investigated by the State Board of Health of 
Massachusetts in connection with the Boston water-supply. Its 
work has shown the strong advisability of diverting the drainage 
of large swamps from a public supply as carrying too much vege- 
table matter even when highly diluted by clear water conforming 
to desirable sanitary standards. 

177. Stripping Reservoir Sites. — The question of stripping or 
cleaning reservoir sites of soil is also one which has been care- 



STRIPPING RESERVOIR SITES. 



223 



fully studied by the Massachusetts State Board of Health. As 
a consequence large amounts of money have been expended by 
the city of Boston in stripping the soil from reservoir sites to the 
average depth in some cases of 9 inches for wooded land and 12^^ 
inches for meadow land. This was done in the case of the 
Nashua River reservoir having a superficial area of 6.56 square 
miles at a cost of early $2,910,000, or about $700 per acre. It 
has been found that the beneficial effect of this stripping is fully 
secured if the black loam in which vegetation flourishes is re- 
moved. 




Wachusetts Reservoir, showing Stripping of Soil. 



This stripping of soil is indicative of the great care taken to 
secure a high quality of water for the city of Boston, but it is not 
done in the Croton watershed of the New York supply. It can- 
not be doubted that the quality of the Croton supply would have 
been sensibly enhanced by a similar treatment of its reservoir 
sites. Mr. F. B. Stearns, chief engineer of the Metropolitan 
Water-supply of Boston, states that in some cases the effects of 
filling reservoirs without removing the soil and vegetable matter 
have ' ' continued for twenty years or more without apparent 
diminution." On the other hand, water discolored by vegetable 



224 



WATER-WORKS FOR CITIES AND TOWNS. 



matter becomes bleached to some extent at least by standing in 
reservoirs whose sites have been stripped of soil. 

178. Average Depth of Reservoirs should be as Great as Prac- 
ticable. — In the selection of reservoir locations those are prefer- 
able where the average depths will be greatest and where shallow 
margins are reduced to a minimum. It may sometimes be 
necessary to excavate marginal portions which would other^vise 
be shallow with a full reservoir. There should be as little water 
as possible of a less low-water depth than 10 or 12 feet, otherwise 
there may be a tendency to aquatic vegetable growth. The 
following table exhibits the areas, average depths, capacity, and 
other features of a number of prominent storage-reservoirs. 

COMPARATIVE TABLE OF AREAS, DEPTHS, AND CAPACITIES OF STORAGE 
RESERVOIRS WITH HEIGHTS AND LENGTHS OF DAMS. 



Name and Location 
of Reservoir. 



Swift River, Mass 

Nashua River, Mass 

Nira, near Poona, India 

Tansa, Bombay, India 

Khadakvasla, Poona, India . . 

New Croton, N. Y 

Elan and Claerwen, Birming- 
ham, Eng. , water- works 
(total for six reservoirs) . . . 

All Boston water-works reser- 
voirs combined 

Vyrnwy, Liverpool, Eng 

Ware River, Mass 

Sodom, N. Y 

Reservoir No. 5, Boston water- 
works 

Titicus, N. Y 

Hobbs Brook, Cambridge 
water- works 

Cochituate, Boston water- 
works 

Reservoir No. 6, Boston 
water- works 



Area. 

Square 

Miles. 



Average 
Depth, 
Feet. 



36.96 
6'. 56 

7-25 
5-5° 
5-50 



2-34 

S.82 

1-75 
1 .62 



1. 91 



1-35 
o. 29 



53 
46 
27 

33 

32 



43 
14 



33 



19 



25 



Maximum Height 
of Dam. 



Above 
Ground. 



- 144 
129 
100 
127 
100 

98-128 

14-65 

84 

71 
72 

65 

105 

23 



52 



Above 
Rock. 



158 



131 
107 
225 



129 



89 

70 
115 



Length 

of Dam, 

Feet. 



2,470 
1,250 
3,000 
8,770 
5,080 
1,270 



4,460 



1.350 

785 
500 

1,865 



1,500 



Capacity, 
Million 
Gallons. 



406,000 
63,o6& 

41,143 
37,500 

36,737 
32,000 



20,838 

15,867 

14,560- 

II, 190 

9,500 

7,438 
7,000 

2,500 

2,160 

1,500 



179. Overturn of Contents of Reservoirs Due to Seasonal 
Changes of Temperature. — It will be noticed that the average 
depth is less than about 20 feet in few cases only. If the water is 



OVERTURN OF CONTENTS OF RESERVOIRS. 225 

deep, its mean temperature throughout the year will be lower 
than if shallow. During the warmer portion of the year the 
upper layers of the water are obviously of a higher temperature 
than the lower portions, since the latter receive much less imme- 
diate effect from the sun's rays. As the upper portions of the 
water are of higher temperature, they are also lighter and hence 
remain at or near the top. For the same reason the water at 
the bottom of the reservoir remains there throughout the warm 
season and until the cool weather of the autumn begins. The 
top layers of water then continue to fall in temperature until it is 
lower than that of the water at the bottom, when the surface- 
water becomes the heaviest and sinks. It displaces subsurface- 
water lighter than itself, the latter coming to the surface to be 
cooled in turn. 

This operation produces a complete overturning of the entire 
reservoir volume as the late autumn or early winter approaches. 
It thus brings to the surface water which has been lying at the 
bottom of the reservoir all summer in contact with what vegetable 
matter may have been there. The depleted oxygen of the 
bottom water is thus replenished with a corresponding better- 
ment of condition. It is the great sanitary effort of nature to 
improve the quality of stored water entrusted to its care, and 
it continues until the surface is cooled to a temperature perh-aps 
lower than that of the greatest density of water. 

Another great turn-over in the water of a lake or reservoir 
covered with ice during the winter occurs in the spring. When 
the ice melts, the resulting water rises a little in temperature 
until it reaches possibly its greatest density at 39°. 2 Fahr., and 
then sinks, displacing subsurface water. This goes on until all 
the ice is melted and until all water cooled by it, near the surface, 
below 39°. 2 Fahr. has been raised to that temperature. The 
period of summer stagnation then follows. 

180. The Construction of Reservoirs. — The natural topography 
and sometimes the geology of the locality determines the loca- 
tion of the reservoir. The first requirement obviously is tight- 
ness. If for any reason whatever, such as leaky banks or bottom, 
porous subsurface material, or for any other defect, the water 
cannot be retained in the reservoir, it is useless. Some very 



226 WATER-WORKS FOR CITIES AND TOWNS. 

perplexing questions in this connection have arisen. Indeed 
reservoirs have been completed only to be found incapable of 
holding their contents. Such results are evidently not creditable 
to the engineers who are responsible for them, and they should 
be avoided. 

YARROW RESERVOIR, UVERPOOL WATER SUPPLY 

i^;^^ . Clay Puddle Core 




Hard Close Shale 

SAN LEANDRO DAM, SAN FRANCISCO WATER WORKS 



t 6"Broien,Stone;^^^^SefeEeiI-Mat£rial^^^ ^TLir^r:::^ I^TT^^^^^— ~^St^.i , 

Riprap ^^^jjasts'^i.—^ — —I °, -". ^^^ °jrj^?!™l?.'ll??3??lfrTir:-~=L 

W7777777yf7777777f7777/7777777777^7777 




TITICUS DAM, NEW YORK WATER SUPPLY' 

El. 334.0 Av 



„ 18 PaTin, 
12~Broken Stone^ 

"^77777^77777777^ 




In order that the bottom of the reservoir may be water-tight 
it must be so well supported by firm underlying material that 
it will not be injured by the weight of water above it, which in 
artificial reservoirs may reach 30 to 100 feet or more in depth. 
The subsurface material at the site of any proposed structure of 
this character must, therefore, be carefully examined so as to 
avoid all porous material, crevasses in rocks, or other open places 
where water might escape. Objectionable material may fre- 
quently be removed and replaced with that which is more suit- 
able, and rock crevices and other open places may sometimes 
be filled with concrete and made satisfactory. Whatever may 
be the conditions existing, the finished bottom of the reservoir 
should be placed only on well-compacted, firm, unyielding 
raaterial. 

The character of the reservoir bottom will depend somewhat 
upon the cost of suitable material of which to construct it. If 



THE CONSTRUCTION OF RESERVOIRS. 327 

a bottom of natural earth cannot be used, a pavement of stone, 
brick, or concrete may be employed from 8 inches to a foot or 
a foot and a half in thickness. The reservoir banks must be 
placed upon carefully prepared foundations, sometimes with 
masonry core walls. They are frequently composed of clayey 
and gravelly material mixed in proper proportions and called 
puddle, although that term is more generally applied to a mixture 
of clay and gravel designed to form a truly impervious wall in 
the centre of the reservoir embankment. Some engineers require 
the core-wall, as it is called, to be constructed of masonry, with 
the earth or gravelly material carried up each side of this wall in 
layers 6 to 9 inches thick, well moistened and each layer thor- 
oughly rolled with a grooved roller, or treated in some equivalent 
manner in order that the whole mass may not be in strata but 
essentially continuous and as nearly impervious as possible. 
The masonry core-wall should- be founded on bed-rock or its 
equivalent. Its thickness will depend upon the height of the 
embankment. If the latter is not more than 20 or 25 feet high, 
the core-wall need not be more than 4 to 6 feet thick, but if the 
embankment reaches a height of 75 feet or even 100 feet, it must 
be made 15 to 20 feet thick, or possibly more, at the base. Its 
top should be not less than 4 or 6 feet thick, imbedded in the 
earth and carried well above the highest surface of water in the 
reservoir. 

The thickness of the clay puddle-wall employed as the central 
core of the reservoir embankment is usually made much thicker 
than that of masonry. As a rough rule it may be made twice 
as thick as the masonry core at the deepest point and not less 
than about 6 feet at the top. The thickness of the puddle core 
is sometimes varied to meet the requirements of the natural 
material in which it is embedded at different depths. 

Frequently, when embankments are under about 20 feet 
high, the core-waUs may be omitted, excavation having been 
made at the base of the embankm.ent down to rock or other im- 
per\4ous material, and if the entire bank is carried up with well- 
selected and puddled material. 

The interior slopes of reservoir embankments are usually 
covered with roughly dressed stone pavement 12 to 18 inches 



228 WATER-WORKS FOR CITIES AND TOWNS. 

thick, laid upon a broken-stone foundation 8 to 12 inches thick, 
for a protection against the wash of waves, the pavement in any 
case being placed upon the bank slope after having been thor- 
oughly and firmly compacted. The sloping and bottom pave- 
ments, of whatever material they may be composed, should be 
made continuous with each other so as to offer no escape for the 
water. In some cases where it has been found difficult to make 
the interior surfaces of reservoirs water-tight, asphalt or other 
similar water-tight layers have been used with excellent results. 

The care necessary to be exercised in the construction of 
storage or other reservoirs when earth dams or embankments 
are used can better be appreciated when it is realized that almost 
all such banks, even when properly provided with masonry or 
clay-puddle core-walls, are saturated with water, even on the 
down-stream side, at least throughout their lower portions. A 
board of engineers appointed by the commissioners of the Croton 
Aqueduct in the summer of 1901 made a large number of exami- 
nations in the earth embankments in the Croton watershed, and 
found that with scarcely an exception those embankments were 
saturated throughout the lower portions of their masses, although 
in every case a masonry core -wall had been built. The results 
of those investigations showed that the water had percolated 
through the earth portion of the embankments and even through 
the core-walls, which had been carried down to bed-rock. This 
induced saturation, more or less, of the material on the down- 
stream slopes of the embankments. When material is thus filled 
with water, unless it is suitably selected, it is apt to become soft 
and unstable, so that any superincumbent weight resting upon it 
might produce failure. The fact that such embankments may 
become saturated with water fixes limits to their heights, since 
the surface of saturation in the interior of the bank hag generally 
a flatter slope than that of the exterior surface. The height of 
the embankment therefore should be such that the exterior slope 
cannot cut into the saturated material at its foot, at least to any 
great extent. From what precedes it is evident that the height 
of an earth embankment will depend largely upon the slope of 
the exterior surface. This slope is made i vertical to 2, 2^, or 3 
horizontal. The more gradual slope is sometimes preferable. 



GATE-HOUSES AND PIPE-LINES IN EMBANKMENTS. 229 

It is advisable also to introduce terraces and to encourage the 
growth of sod so as to protect the surface from wash. The inner 
paved slope may be as steep as i vertical to i^ or 2 horizontal. 

BOG EROOK. DAM NO. 1.— RESERVOIR I. 

No. 1-^ /No. 2 




TITICUS DAM.— RESERVOIR M. 
Top of Spillway 



/-No. 4 




AMAWALK_DAM. — RESERVOIR A. 




14.7 pep 100 
No. 13 „ 



Earth Dams in Croton Watershed, showing Slopes of Saturation. 

i8i. Gate-houses, and Pipe-lines in Embankments. — It is 
necessary to construct the requisite pipe-lines and conduits lead- 
ing from the storage-reservoirs to the points of consumption, and 
sometimes such lines bring the water to the reservoir. Wherever 
such pipes-line or conduits either enter or leave a reservoir gates 
and valves must be provided so as properly to control the ad- 
mission and outflow of the water. These gate-houses, as they 
are called, because they contain the gates or valves and such 
other appurtenances or details as are requisite for operation and 
maintenance, are usually built of substantial masonry. They 
are the special outward features of every reservoir construction, 
and their architecture should be characteristic and suitable to 
the functions which they perform. Where the pipes are carried 
through embankments it is necessary to use special precautions 
to prevent the water from flowing along their exterior surfaces. 
Many reservoirs have been constructed under defective design 
in this respect, and their embankments have failed. Frequently 



230 WATER-WORKS FOR CITIES AND TOWNS. 

small masonry walls are built around the pipes and imbedded 
in the bank, so as to form stops for any initial streams of water 
that might find their way along the pipe. In short, every care 
and resource known to the civil engineer must be employed in 
reservoir construction to make its bottom and its banks proof 
against leakage and to secure permanence and stability in every 
feature. 

182. High Masonry Dams. — The greatest depths of water 
impounded in reservoirs are found usually where it is necessary 
to construct a high dam across the course of a river, as at the new 
Croton dam. In such cases it is not uncommon to require a 
dam over 75 to 100 feet high above the original bed of the river, 
which is usually constructed of masonry with foundations car- 
ried down to bed-rock in order to secure suitable stability and 
prevent flow or leakage beneath the structure. It is necessary 
to secure that result not only along the foundation-bed of the 
dam, but around its ends, and special care is taken in those por- 
tions of the work. 

The new Croton dam is the highest masonry structure of its 
class yet built. The crest of its masonry overflow-weir is 149 
feet above the original river-bed, with the extreme top of the 
masonry work of the remaining portion of the dam carried 14 
feet higher. A depth of earth and rock excavation of 131 feet 
below the river-bed was necessary in order to secure a suitable 
foundation on bed-rock. The total maximum height, therefore, 
of the new Croton dam, from the lowest foundation-point to 
the extreme top, is 294 feet, and the depth of wat^r at the 
up-stream face of the dam will be 136 feet when the overflow is 
just beginning, or 140 feet if 4 feet additional head be secured 
by the use of flash-boards. In the prosecution of this class of 
work it is necessary not only to reach bed-rock, but to remove 
all soft portions of it down to sound hard material, to clean out 
all crevices and fissures of sensible size, refilling them with 
hydraulic cement mortar or concrete, and to shape the exposed 
rock surfaces so as to make them at least approximately normal 
to the resultant loads upon them, to secure a complete and 
as nearly as possible water-tight bond with the superimposed 
masonry. If any streams or other small watercourses should 



HIGH MASONRY DAMS. 



231 



be encountered, they must either be stopped or led off where they 
will not affect the work, or, as is sometimes done, the water 
issuing from them may be carried safely through the masonry 



SECTION 

or 
AfEW CROTON DAM 



ELE.. 196. OVERFLOW. 




Cross-section of New Cioton Dam. 

mass in small pipes. The object is to keep as much water out 
of the foundation-bed as possible, so as to eliminate upward 
pressure underneath the dam caused by the head of water in 
the subsequently full reservoir. It is a question how much 
dependence can be placed upon the exclusion of water from the 
foundation-bed. In the best class of work undoubtedly the 
bond can be good enough to exclude more or less water, but it 
is probably only safe and prudent so to design the dam as to be 
stable even though water be not fully excluded. 

The stability of the masonry dam must be secured both for 
the reservoir full and empty. With a full reservoir the hori- 
zontal pressure of water on the up-stream face tends to overturn 



233 WATER-WORKS FOR CITIES AND TOWNS. 

the dam down-stream. When the water is entirely withdrawn 
the pressure under the up-stream edge of the foundation becomes 
much greater, so that safety and stabihty under both extreme 
conditions must be assured. There are a number of systems of 
computation to which engineers resort in order to secure a design 
which shall certainly be stable under all conditions. That which 
is commonly employed in this country is based upon two funda- 
mental propositions, under one of which the pressure at any 
point in the entire masonry mass must not exceed a certain safe 
amount per square foot, while the other is of a more technical 
character, requiring that the centre of pressure shall, in every 
horizontal plane of the dam, approach nowhere nearer than one 
third the horizontal thickness of the masonry to one edge of it. 
A further condition is also prescribed which prevents any por- 
tion of the dam from slipping or sliding over that below it. As 
a matter of fact when the first two conditions are assured the 
third is usually fulfilled concurrently. Obviously there will be 
great advantage accruing to a dam if the entire mass of masonry 
is essentially monolithic. In order that that may be the case 
either concrete or rubble is usually employed for the great mass 
of the masonry structure, the exterior surfaces frequently being 
composed of a shell of cut stone, so as to provide a neat and taste- 
ful finish. This exterior skin or layer of cut masonry need not 
average more than i|- to 2^ feet thick. 

The pressures prescribed for safety in the construction of 
masonry dams vary from about 16,000 to 28,000 or 30,000 pounds 
per square foot. Sometimes, as in the masonry dams found in 
the Croton watershed, limits of 16,000 to 20,000 pounds per 
square foot are prescribed for the upper portions of the dams 
and a gradually increasing pressure up to 30,000 pounds per 
square foot in passing downward to the foundation-bed. There 
are reasons of a purely technical character why the prescribed 
safe working pressure must be taken less on the down-stream 
or front side of the dam than on the up-stream or rear face. 

The section of a masonry dam designed under the conditions 
outlined will secure stability through the weight of the structure 
alone, hence it is called a gravity section. In some cases the 
rock bed and sides of a ravine in which the stream must be 



HIGH MASONRY DAMS. 233 

dammed will permit a curved structure to be built, the curva- 
ture being so placed as to be convex up-stream or against the 
water pressure. In such a case the dam really becomes a hori- 




Foundation Masonry of New Croton Dam. 

zontal arch and, if the curvature is sufficiently sharp, it may be 
designed as an arch horizontally pressed. The cross-section 
then has much less thickness (and hence less area) than if de- 
signed on a straight line so as to produce a gravity section. A 
number of such dams have been built, and one very remarkable 
example of its kind is the Bear Valley dam in California ; it was 
built as a part of the irrigation system. 



CHAPTER XVII. 

183.- Gravity Supplies. — ^When investigation has shown that 
a sufficient quantity of water may be obtained for a required 
pubHc supply from any of the sources to which reference has 
been made, and that a sufficient storage capacity may be pro- 
vided to meet the exigencies of low rainfall years, it will be evi- 
dent if the water can be delivered to the points of consumption by 
gravity, or whether pumping must be employed, or recourse be 
made to both agencies. 

If the elevation of the source of supply is sufficiently great 
to permit the water to flow by gravity either to storage-reser- 
voirs or to service-reservoirs and thence to the points of con- 
sumption, a proper pipe-line or conduit must be designed to 
afford a suitable channel. If the topography permits, a conduit 
may be laid which does not run full, but which has sufficient 
grade or slope to induce the water to flow in it as if it were 
an open channel. This is the character of such great closed 
masonry channels as the new and old Croton aqueducts of the New 
York water-supply and the Sudbury and Wachusetts aqueducts 
of the Boston supply. These conduits are of brick masonry 
backed with concrete carried sometimes on embankments and 
sometimes through rock tunnels. When they act like open chan- 
nels a very small slope is employed, 0.7 of a foot per mile being a 
ruling gradient for the new Croton aqueduct, and i foot per mile 
for the Sudbury. Where these conduits cross depressions and 
follow approximately the surface, or where they pass under rivers, 
their construction must be changed so that they will not only 
run full, but under greater or less pressure, as the case may be. 

184. Masonry Conduits. — In general the conduits employed 
to bring water from the watersheds to reservoirs at or near places 

234 



MASONRY CONDUITS. 235 

of consumption may be divided into two classes, masonry and 
metal, although timber-stave pipes of large diameter are much 
used in the western portion of the country. The masonry con- 
duits obviously cannot be permitted to run full, meaning under 
pressure, for the reason that masonry is not adapted to resist 
the tension which would be created under the head or pressure 
of water induced in the full pipe. They must rather be so em- 
ployed as to permit the water to flow with its upper surface 
exposed to the atmosphere, although masonry conduits are 
always closed at the top. In other words, they must be per- 
mitted to run partially full, the natural grade or slope of the 
water surface in them inducing the necessary velocity of flow 
or current. Evidently the velocity in such masonry conduits 
is comparatively small, seldom exceeding about 3 feet per second. 
The new and old Croton aqueducts, the Sudbury and Wachu- 
setts aqueducts of the . Metropolitan Water-supply of Boston, 
are excellent types of such conveyors of water. They are some- 
times of circular shape, but more frequently of the horseshoe 
outline for the sides and top, with an inverted arch at the bottom 
for the purpose of some concentration of flow when a small 
amount of water is being discharged and for structural reasons. 
The interiors of these conduits are either constructed of brick 
or they may be of concrete or other masonry affording smooth 
surfaces. In the latest construction Portland-cement concrete 
or that concrete reinforced with light rods of iron or steel is much 
used. Bricks, if employed, should be of good quality and laid 
accurately to the outline desired with about |-inch joints, so as 
to offer as smooth a surface as possible for the water to flow over. 
In special cases the interiors of these conduits may be finished 
with a smooth coating of Portland -cement mortar. If conduits 
are supported on embankments, great care must be exercised 
in constructing their foundation supports, since any sensible 
settlement would be likely to form cracks through which much 
water might easily escape. When carried through tunnels they 
are frequently made circular in outline. They must occasionally 
be cleaned, especially in view of the fact that low orders of vege- 
table growths appear on their sides and so obstruct the free flow 
of water. 



330 WATER-WORKS FOR CITIES AND TOWNS. 

185. Metal Conduits. — Metal conduits have been much used 
within the past fifteen or twenty years. Among the most promi- 
nent of these are the Hemlock Lake aqueduct of the Rochester 
Water-works, and that of the East Jersey Water Company 
through which the water-supply of the city of Newark, N. J., 
flows. When these metal conduits or pipes equal 24 to 30 or more 
inches in diameter they are usually made of steel plates, the latter 
being of such thickness as is required to resist the pressure acting 
within them. The riveted sections of these pipes may be of 
cylindrical shape, each alternate section being sufficiently small 
in diameter just to enter the other alternate sections of little 
larger diameter, the interior diameter of the larger sections 
obviously being equal to the interior diameter of the smaller 
sections plus twice the thickness of the plate. Each section 
may also be slightly conical in shape, the larger ends having a 
diameter just large enough to pass sufiiciently over the smaller 
end of the next section to form a joint. Large cast-iron pipes 
are also sometimes used to form these metal conduits up to an 
interior diameter of 48 inches. The selection of the type of con- 
duit within the limits of diameter adapted to both metals is 
usually made a matter of economy. The interior of the cast-iron 
pipe is smoother than that of the riveted steel, although this is 
not a serious matter in deciding upon the type of pipe to be 
used. 

Steel-plate conduits have been manufactured and used up 
to a diameter of 9 feet. In this case the pipe was used in 
connection with water-power purposes and with a length of 
153 feet only, the plates being ^ inch thick. The steel-plate 
conduits of the East Jersey Water Company's pipes are as 
follows : 



Diameter. 


Thickness. 


Length 


48 inches 


I inch 




48 " 


A" ■•■ 


. . 21 miles, 


48 " 


f " J 




36 " 


1 " 

i • • • 


... 5 " 



The diameters and lengths of the metal pipes or conduits of 



GENERAL FORMULA FOR DL'^CHARGE OF CONDUITS. 237 

the Hemlock Lake conduit of the Rochester Water-works are as 

follows : 

3 6 -inch wrought-iron pipe. . 9.60 miles. 
24 " " " .. 2.96 " 
24 " cast-iron pipe 15-82 " 



Total 28.39 " 

All metal conduits or pipes are carefully coated with a suit- 
able asphalt or tar preparation or varnish applied hot and 
sometimes baked before being put in place. This is for the 
purpose of protecting the metal against corrosion. Cast-iron 
pipes have been used longer and much more extensively than 
wrought iron Qr steel, but an experience extending over thirty 
to forty years has shown that the latter class of pipes possesses 
satisfactory durability and may be used to advantage whenever 
economical considerations may be served. 

186. General Formula for Discharge of Conduits — Chezy's 
Formula. — It is imperative in designing aqueducts of either 
masonry or metal to determine their discharging capacity, which 
in general will depend largely upon the slope of channel or head 
of water and the resistance offered by the bed or interior of the 
pipe to the flow of water. The resistance of liquid friction is 
so much more than all others in this class of water-conveyors 
that it is usually the only one considered. There is a certain 
formula much used by civil engineers for this purpose; it is 
known as Chezy's formula, for the reason that it was first estab- 
lished by the French engineer Antoine Chezy about -the year 1775, 
although it is an open question whether the beginnings of the 
formula were not made twenty or more years prior to that date. 
Its demonstration involves the general consideration of the 
resistance which a liquid meets in flowing over any surface, such 
as that of the interior of a pipe or conduit, or the bed and banks 
of a stream. 

The force of liquid friction is found to be proportional to the 
heaviness of the liquid (i.e., to the weight of a cubic unit, such 
as a cubic foot) , to the area of wetted surface over which the liquid 
flows, and nearly to the square of the velocity with which the 



238 



WATER-WORKS FOR CITIES AND TOWNS. 



liquid moves. Hence if /' is the length of channel, p the wetted 
portion of the perimeter of the cross-section, w the weight of a 
cubic unit of the liquid, and v the velocity, the total force of 
liquid friction for the length /' of channel will be F = Cii'pVv^, 
C being the coefficient of liquid friction. The path of the force 




Fig. 2. 



F for a unit of time is v, and the work W which it performs in 
that unit of time is equal to the weight waV falling through the 
height h\ a being the area of the cross -section of the stream. 



Hence 



W = Cwpl'v^.v =wal'h' (7) 

. . . (8) 



9 ^7/ hah' 



Zp V 



In this equation 



c = A,-; r=-= hydraulic mean radius ; 

C P 

h' 
s = — = sine of inclination of stream's bed. 

V 



As the motion of the water is assumed to be uniform, the head 
lost by friction for the total length of channel / is the total fall h, 

and by equation (8) , smce — =s=j, 



h=—T—. 
c^ a 

P 



(9) 



KUTTER'S FORMULA. 239 

If, as in the case of the ordinary cast-iron water-pipes of a pubhc 
supply system, the cross-section a is circular, 

a A ci 



and 



4 

P 7ld 4 



4.2glv' Iv' 
c^ d 2g ' d 2g ^ ^ 



in which f = Sg-^ c^. 

The quantity / is sometimes called the "friction factor." 
For smooth, new pipes from 4 feet down to 3 inches in diameter 
its value may be taken from .015 to .03. An approximate mean 
value may be taken at .02. 

The last member of equation (8) is Chezy's formula, and it is 
one of the most used expressions in hydraulic engineering. 
Some values for the coefficient c will presently be given. The 
quantity r found by dividing the area of the cross-section of the 
stream by the wetted portion of its perimeter is called the ' ' hy- 
draulic mean radius,"" or simply the ' 'mean radius." The other 
quantity, s, appearing in the formula is, as shown by the figure, 
the sine of the inclination of the bed of the stream. 

In order to determine the discharge of any pipe, conduit, or 
open channel carrying a known depth of water, it is only necessary 
to compute r and s from known data and select such a value of 
the coefficient c as may best fit the circumstances of the particu- 
lar case in question. The substitution of those quantities in 
Chezy's formula, i.e., equation (8), will give the mean velocity v 
of the water which, when multiplied by the area of cross-section 
of the stream, will give the discharge of the latter per second of 
time. It is customary to compute r in feet. The coefficient c 
is always determined so as to give velocity in feet per second of 
time. Hence if the area of the cross-section of the stream, a, 
is taken in square feet, as is ordinarily the case, the discharge av 
will be in cubic feet per second. 

187. Kutter's Formula. — The coefficient c in Chezy's formula is 
not a constant quantity, but it varies with the mean radus r, with 
the sine of inclination s, and with the character of the bottom 



340 



WATER-WORKS FOR CITIES AND TOWNS. 



and sides of the open channel, i.e., with the roughness of the 
interior surface of the closed pipe. Many efforts have been made 
and much labor expended in order to find an expression for this 
coefficient which may accurately fit various streams and pipes. 
These efforts have met with only a moderate degree of success. 




Progress View of Construction of New Croton Dam. 

The form of expression for c which is used most among engineers 
is that known as Kutter's formula, as it was established by the 
Swiss engineer W. R. Kutter. This formula is as follows: 



v? 



c = 



n 



'1.511 , .OO20IN 

+ 41.65 H 

n ^ ^ s 

Vr .00281 
+ 41.65 + 



The quantity n in this formula is called the ' ' coefficient of rough- 
ness," since its value depends upon the character of the surface 



HYDRAULIC GRADIENT. 241 

over which the water jEiows. It has the following set of values 
for the surfaces indicated : 

n =0.009 tor well-planed timber; 

« =0.010 for neat cement; 

n = o.oi I for cement with one third sand ; 

w = o.oi 2 for unplaned timber ; 

w = 0.013 for ashlar and brickwork; 

w =0.015 for unclean surfaces in sewers and conduits; 

n = o.oi'j for rubble masonry ; 

w = 0.020 for canals in very firm gravel ; 

n = 0.025 for canals and rivers free from stones and weeds ; 

n = 0.030 for canals and rivers with some stones and weeds ; 

w = 0.035 for canals and rivers in bad order. 

188. Hydraulic Gradient. — Before illustrating the use of 
Chezy's formula in connection with masonry and metal conduits, 
of which mention has already' been made, it is best to define 
another quantity constantly used in connection with closed iron 
or steel pipes. This quantity is called the ' ' hydraulic gradient." 
If a closed iron or steel pipe is running full of water and under 
pressure and if small vertical tubes be inserted in the top of the 
pipe with their lower ends bent so as to be at right angles 
to its axis, the water will rise to heights in the tubes depending 
upon the pressures of water in the pipe or conduit at the 
points of insertion. Such tubes with the water columns in 
them are called piezometers. They are constantly used in con- 
nection with water-pipes in order to show the pressures at the 
points where they are inserted. A number of such pipes being 
inserted along an iron pipe or conduit, a line may be imagined 
to be drawn through the upper surfaces of the columns of water, 
and that line is called the "hydraulic gradient." It represents 
the upper surface of water in an open channel discharging with 
the same velocity existing in the closed pipe. 

In case Chezy's formula is used to determine the velocity of 
discharge in a closed pipe running under pressure, the sine of 
inclination 5 must be that of the hydraulic gradient and not the 
sine of inclination of the axis of the closed pipe. In the deter- 
mination of this quantity 5 by the use of piezometer tubes, if a 



243 



WATER-WORKS FOR CITIES AND TOWNS. 



straight pipe remains of constant section between any two points, 
it is only necessary to insert the tubes at those points and observe 
the difference in levels of the water columns in them. That 
difference of levels or elevations will represent the height which 
is to be divided by the length of pipe or conduit between the 
same two points in order to determine the sine .?. 

The hydraulic gradient plays a very important part in the con- 
struction of a long pipe-line or conduit. If any part of the pipe 
should rise above the hydraulic gradient, the discharge would 
no longer be full below that point. It is necessary, therefore, 
always to lay the pipe or the closed conduit so that all parts of 






--iii 



l^jfittifaa^^, -'aKg 




Progress View of Construction of New Croton Dam. 

it shall be below the hydraulic gradient. Caution is obviously 
necessary to lay a pipe carrying water deep enough below the 
surface of the ground in cold climates to protect the water against 
freezing. At the same time if the pipe-line is a long one it must 
follow the surface of the ground approximately in order to save 



HYDRAULIC GRADIENT. 



243 



Locafion of lead 
wafer- s fop af jolnfs 
befween secfions 
of arch. 




2B'-7i" — 

IN LOOSE EARTH. 




IN ROCK. H^rd packed rock debris 

Weston Aqueduct. Sections of Aqueduct and Embankment. 



344 



WATER-WORKS FOR CITIES AND TOWNS. 



expensive cutting. There will, therefore, generally be summits 
in pipe-lines, and inasmuch as all potable water carries some air 
dissolved in it, that air is liable to accumulate at the high points 




SECTION OF EMBANKMENT. 



4 8 12 16 




j. ,3--0i 

ON EMBANKMENT. 

Weston Aqueduct. Sections of Aqueduct and Embanknaent. Gradient, i in 5000. 

or summits. If that accumulation goes on long enough, it will 
seriously trench upon the carrying capacity of the pipe and de- 
crease its flow. It is therefore necessary to provide at summits 
what are called blow-off cocks to let the air escape. At the low 
points of the pipe-line, on the contrary, the solid matter, such as 
sand and dirt, carried by the water is liable to accumulate, and 
it is customary to arrange blow-offs also at such points, so as 
to enable some of the water to escape and carry with it the sand 
and dirt. 

189. Flow of Water in Large Masonry Conduits. — In order to 
apply Chezy's formula first to the flow of the masonry aqueducts 
of the New York and Boston water-supplies, it is necessary to 
have the outlines of those conduits so that the wetted perimeter 
and hence the mean radius may be determined for any depth 
of water in them. 



FLOW OF WATER THROUGH LARGE CLOSED PIPES. 245 

The figure shows the desired cross-sections drawn carefully to 
scale. Table XIV has been computed and arranged from data 
taken from various official sources so as to show the depth, 



-N E-W-C ROTO N— 1 316- 
-WESTON— 13.1-7^ 




OUTUNETS OF AQUEDUCTS 



Fig. 3- 



mean velocity, discharge per second and per twenty-four hours, 
and the coefficient used in Chezy's formula, together with the 
coefficient of roughness n in Kutter's formula for the conduits 
shown in the figure. 

This table exhibits in a concise and clear manner the use of 
Chezy's formula in this class of hydraulic work. 

190. Flow of Water through Large Closed Pipes. — The ma- 
sonry conduits to which consideration has been given in the pre- 
ceding paragraphs carry water precisely as in an open canal, 
but the closed conduits or pipes of steel plates and cast iron, like 
the Hemlock Lake conduit at Rochester and the East Jersey 
conduit of the Newark Water-works, are of an entirely different 



246 



WATER-WORKS FOR CITIES -AND TOWNS. 



TABLE XIV. 





Depth, 

in 
Feet. 


2 
■'3 

cS ,- 
u ^ 


Grade 
s. 


1 




> . 

03 CD 


Discharge. 




Aqueducts. 


dj 

rv, 

5ft 


Gallons 
per 24 Hours. 


u 

MS 

CO 


* New Croton (1899) 

* " " (after two 

years' use) 


8.42 


3-974 

2-338 
I 

i-S 
2 

2-5 

3 

3-5 
4 
2-338 

2-338 
2.368 
1.87s 
2.338 


.0001326 


153-3 

131 -3 

II9-3 

126.3 

129.8 

132 

133-4 

134 

134.4 

133-4 

123-2 
118. 2 
119 
125-0 

144-9 
116. 9 
127.0 
133-3 
137-8 
140.4 


3-52 
2.312 

1-374 

1. 781 

2. 114 

2.404 
2.661 

2.887 
3-095 

2-958 


37^-6 


240,200,000 


. 0133 


122.8 


79,400,000 

73,300,000 
85,600,000 




J. 1 > II 






*■ '• " 






J. 1 1 > ' 






J. ■ ' " 






J. < . 11 






■j- " " . 






Old Croton (1899) clean....... 

" " ordinary condi- 


6 

6 
7-33 


-0133 


" " not clean 

Dorchester Bay tunnel 












.014 


Wachusetts, new; probably 




1. 14 
1.74 
2.24 

2.68 
3-04 












• 5 
I - 
I. 5 
2 . 

2.5 


. 000189 










■ 1 • 1 






■ < •< 






• 1 1 1 













* From report by J. R. Freeman to B. S. Coler, 1899. 
t From report of New York Aqueduct Commission. 



type, as they carry water under pressure. Hence the slope or 
sine of inchnation 5 belongs to the hydraulic gradient rather 
than to the grade of the pipe itself. Where the pipe-line is a long 
one its average grade frequently does not differ much from the 
hydrauhc gradient, but the latter quantity must always be used. 
As in the case of the masonry conduits, the coefficient c in Chezy's 
formula will vary considerably with the degree of roughness 
of the interior surface of the pipe, with the slope s, and with the 
mean radius r. An important distinction must be made between 
riveted steel pipes and those of cast iron, for the reason that the 
rivet-heads on the inside of the former exert an appreciable 
influence upon the coefficient c. The rivet-heads add to the 
roughness or unevenness of the interior of the pipe. Table XV 
gives the elements of the flow or discharge in the two pipe-lines 
which have been taken as types, as determined by actual meas- 



FLOW OF WATER THROUGH LARGE CLOSED PIPES. 



247 



urements; it also exhibits similar elements for timber-stave 
pipes, to which reference will be made later. 




As would be expected, the velocity of flow in these pipes may 
be and generally is considerably higher than the velocity of 
movement in masonry channels. Both Tables XV and XVI 
give considerable range of coefficients computed and arranged 
from authoritative sources, and the coefficients c for Chezy's 
formula represent the best hydraulic practice in connection 
with such works at the present time. In using the formula 
for any special case, great care must be taken to select a value 
for c which has been established for conditions as closely as 
possible to those in question. This is essential in order that the 
results of estimated discharges may not be disappointing, as 
they sometimes have been where that condition so necessary to 
accuracy has not been fulfilled. 



248 



WATEE-WORKS FOR CITIES AND TOWNS. 



TABLE XV. 
VALUES OF COEFFICIENT C. 



Pipe-line. 



Diameter. 



Hydraulic 
Radius 



Hydraulic 
Gradient. 



Mean 
Velocity. 



Hemlock Lake 

Rush Lake to Mt. Hope 

Sudbury aqueduct 

East Jersey Water Co 

Timber-stave pipe, Ogden, Utah 



36" wrought iron 
24" wr't and cast 
24" cast iron 



48" 
48" 
48" 



48" 

48" steel riveted 
pipe 

'■5 
'•5 
'•5 
'■5 
'■5 
■-5 
'•5 



9" 
6" 
6" 



.000411 

.00239 

■00255 



12 
12" 



3 

n 



72 
72 

72 
72' 

li' 
72 

72" 



1-532 
3-448 
448 
738 
965 
195 
738 
965 
195 
62 

5 

o 

5 

5 
3 

3-5 
4 



Pipe-line. 



Coefficient 



Discharge. 



Cubic Feet 
per Second. 



Gallons 
per 24Hours. 



Remarks. 



Hemlock Lake 

Rush Lake to Mt. Hope 

Sudbury aqueduct 

<i (( 

<( (I 

<< (I 

C( it 

East Jersey Water Co 

Timber-stave pipe, Ogden, Utah 



87-3 

99-7 

96-5 

140 . 14 

142 . II 

144.09 



139.94=^. 
141 .74*. 
143.16*. 



10 . 83124 
10 .83124 
10 .83124 



7,000,000 
7,000,000 
7,000,000 



103. 
72 
96 

109 

115 
119 
122 
124 
126 



58. 



37,500,000 



1892. 

' Pipe new 
j" 1880. 

After 
cleaning, 
1894-95. 
1 Before 
1 cleaning, 
) f = 108 
1891. 
1897. 



* These values correspond to the formula c=i3i.8Sv''°'^^' 



FLOW OF WATER THROUGH LARGE CLOSED PIPES. 



249 



V 



> 

X 


2; 


f^ 




H-1 


n 


< 




H 


W 




P 




J 




<5 




> 



« 


nj 





o 


o 


r^ 


O 


00 

00 




o 






0\ 

VO 


M 




vO 


M 


vO 














2 


1 


i^ 


OOmOCOCO O !-•• 

„„„„00 M M. 


o 


" 




00 

1- 




• Tf 

r^COOMN ro -rt •!)■ ir, \n m " 
OOOOO OOOOO 


o 


03 


CO 




WOOfTJOrO CO t^f^r^I^ 

• .... ^ 

t^OrOti/1 •* ^^OrO^^rO " 
OvOOOO O OOOOO O 


o> 




■00 




. . . o . .... o 

«) Tf Ov N rO Tj- Tt Tt Tf Tj- M 

t^OOCOO 0\ O0*0\C>0n o 


00 




00 




« Tj-00 MOO ■* N Tf t^vO 
• ■ • • • ro 

M lOOO MM fO C^<N<NMM M 
OOOMM M MMMMM Q 


t^ 


u 
^ 


^ 




oOcoiTitj-- N OON -tioin 

• ■ • • ■ fO 

M CN Tj- U-jO I^ X^GO OC CO go M 

OOOOO O OOOOO O 


vO 


1 


^ 




O O CO 00 00 N 

vOroi^MN ro WmOOO m 
OOOmm m mhmmm o 


:. 




M- 








o> 
















o 


Tj- 




















o 













m 








ro 


CD 


CO 




























o 


« 




to 


























VO 

o 









" 




VO 




• O O lO 
■CO C> Ov 


■t fO 

o o 




o 


VO 

o T^ 


« rt-vo 

... Tl- 
r- O fO M 

M N M 






^ 


6 
2; 


-< 


•i-^/V :; = /2 ui ;» 






d 

!> 0) 
fa 


c 


3 t- 


00 


-i O T 


■ u 


^^ 


■> c 


1 ^ 

1 f 


ro 1/ 


■) m C 




t T 


1 c 
1- r: 


l-u 




IvC 


II 4^ S 

s? c c 

^8-o 



'AC 






.C O-M M g 



OJ 



O 3 O j3 



0^3 '■^ - 



7^-d'f^-S rt o 
? c OJ -pq -ffi 

S:*7'-^ VO*^ On On 

O"^ f Ov 00 . CO . 






<u t« "~ 






u§o 



05 U3 . W . W . - ■ 

ooooooooo 

^; 2; 2: 2:^2; 2; 22; 



250 



WATER-WORKS FOR CITIES AND TOWNS. 



191. Change of Hydraulic Gradient by Changing Diameter of 
Pipe. — It has already been seen, in the case of closed pipes or 
conduits, that the hydraulic gradient with slope 5 governs the 
velocity of flow, and also that all parts of the pipe-line must be 
kept below that gradient. It is sometimes desirable, in order to 













CROTON AQUEDUCT 








IN ROCK. 




J 






l^% 


Wlr.-=.-^- 


'^^9 




" 


J 


^^^pBBB^^faTg^jSj^- 


^^s^ 






V 


^^^^sj^^nm^^^^^ 


|B 






/ 


^^^C 


ymaSf^A 






/ 


/j^^|3H 


- i ^ 




^ ittJ^SCw^^LZ'' ''"t.K 


"■ ^2^t^m 


'i^^<r- ■ ' 


1^60 


•■ ^ ^t^$llf^^i/ 


<^*- -^^^m^M 


? - ^ 


. 


^ irtiVi^^^^^)/^ 


c'V^^^I 


ill 


':;' 


Sw^^^ 


'^^B 


B i 


1 


^^» 


^Sm. .',?j ij^ 


K^^* f 




^jv-.-n'e ; 


I 


^^^mA^^^K, 




^^o?** '^^Sa^''^^^ 


^■BS 


i 


j^^nP' "^ <il iE^Mi^^^ 


^^^^^S 


l^^^l?. / 


1 


^«<^^jtH(Mftt^^^K- 


^^m 






^^^^S^R- 


QBTUunWraroSSffl^^E! 




^^kSSSs^^^T^^^^^ 






^ 






iS^^^s^S^^ 


^w^^^^^ 










^^^^^^l^^'^ 





meet conditions either of topography or of flow, to raise or lower 
the hydraulic gradient over the whole or some portion of the 
pipe-line. This can easily be done to any needed extent by 
varying the diameter of the pipe. An increase in diameter will 
in general decrease the velocity of the water and increase its 
pressure, thus increasing correspondingly the height of the col- 
umns of water in the piezometer-tubes. As the top surface of 
the latter determines the hydraulic gradient, it is seen that in- 
creasing the diameter of a portion of the pipe-line will corre- 
spondingly raise the gradient over the same portion. Thus by 



CONTROL OF FLOW IN METAL CONDUITS BY GATES. 351 

a proper relative variation of diameters the hydraulic gradient 
of a given pipe-line may readily be controlled within sufficient 
limits to meet any ordinary requirements of this character. 

192. Control of Flow by Gates at Upper End of Pipe-line. — 
Obviously, if the pressure in the pipe-line is diminished, less thick- 
ness of metal will be required to resist it, and a corresponding 
degree of economy may be reached by a decrease in the quantity 
of metal. In the 21 miles of 48 -inch steel-plate pipe of the East 
Jersey Water Company there is a fall of 340 feet; if, therefore, 
the flow through that pipe were regulated by a gate or gates at 
its lower end, the lower portion of the line would be subjected 
to great intensity of pressure. If, however, the flow through 
the pipe is controlled by a gate or gates at its upper end, enough 
water only may be admitted to enable it to flow full with the 
velocity due to the hydraulic gradient. By such a procedure 
the pressure upon the pipe over and above that which is necessary 
to produce the gradient is avoided. This condition is not only 
judicious in the reduction of the amount of metal required, but 
also in reducing both the leakage and the tendency to further 
leakage, which is largely increased by high pressures. This fea- 
ture of control of pressure in a long pipe-line with considerable 
fall is always worthy of most careful consideration. 

193. Flow in Old and New Cast-iron Pipes — Tubercles. — The 
velocity of flow through cast-iron mains or conduits or through 
the cast-iron pipes of a distribution system of public water- 
supply depends largely upon the condition of the interior surface 
of the pipes as affected by age. All cast-iron pipes' before being 
shipped from the foundry where they are manufactured are 
immersed in a hot bath of suitable coal-tar pitch composition in 
order to protect them from corrosion. After having been in 
use a few years this coating on the interior of the pipes is worn 
off in spots and corrosion at once begins. The iron oxide pro- 
duced under these circumstances forms projections, or tubercles 
as they are called, of greatly exaggerated volume and out of all 
proportion to the actual weight of oxide of iron. When the 
pipes are emptied these tubercles are readily removed by scrap- 
ing, but before their removal they greatly obstruct the flow of 
water through the pipes. Indeed this obstruction is so great 



252 



WATER-WORKS FOR CITIES AND TOWNS. 



that the discharging capacity of cast-iron mains must be treated 
in view of its depreciation from this source. 

Table XVII exhibits the value of the coefficient c to be used 
in Chezy's formula for all cast-iron pipes having been in use for 
the periods shown. 



TABLE XVII. 
TABLE OF VALUES OF jT AND C. 



Authority. 


Pipe-line. 


Diameter, 
Inches. 


Hydraulic 
Radius 

r, 
Inches. 


Velocity, 
Feet per 
Second. 


Coefficient 
e. 


Coefficient 


Darcy 
Darcy \ 
Darcy 
Brush j 
Darrach < 
Darrach ■ 


New pipe 

Old cast-iron pipe lined j 
with deposit [ 

Pipe above cleaned 

Cast-iron pipe tar-coated ) 

and in service 5 years. ) 

Cast-iron pipe in service ) 

II years J 

Cast-iron pipe in service ) 

7 years \ 


3.22 
9.63 
9-63 

20 

20 

36 


.8 
2.41 
2.41 

5 
5 
9 


j 0.29 
1 10.71 
j I.OO 

I 12.42 
\ 0.91 

/ 14.75 

j 2.00 

1 3.00 
J 2.71 

1 5-II 
j 1.58 
i 2.37 


78.5 
100. 

72.5 
74.0 
90.0 
98.0 
114. 
IIO.O 

67.5 
83.0 

60.0 

66.0 


.0418 
.0257 
.0489 
.0468 
.0316 
.0269 
.0197 
.0214 
.0568 
.0376 
.0716 
.0586 



Obviously it is not possible to clean the smaller pipes of a 
distribution system, but large cast-iron conduits may be emptied 
at suitable periods and have their interior surfaces cleaned of 
tubercles or other accumulations. At the same time, if necessary, 
a new coal-tar coating can be applied. 

Table XVIII exhibits the values of the coefficient c to be 
used in Chezy's formula for new and clean coated cast-iron pipes. 
It represents the results of actual hydraulic experience and is 
taken from Hamilton Smith's "Hydraulics." A comparison 
between this table and that which precedes will show how serious 
the effect of tubercles may be on the discharging capacity of a 
cast-iron pipe. 

In using Chezy's formula, v = c\/ts, in connection with either 
Table XVII or XVIII, the slope or sine of inclination 5 of the 
hydraulic gradient may be readily computed by equation (lo), 
which gives the head lost by friction in a closed circular pipe as 



TIMBER-STAVE PIPES. 



253 



TABLE XVIII. 

VALUES OF C IN FORMULA: V = c^rs. 





Diameters in Feet ((/=4r). 


.05 


. I 


I 


i-S 


2 


2.S 


3 


Z-S 


4 


S 


6 


7 i 8 


> 


























I 




80.0 


96 . 1 


102.8 


108.8 


112 .7 


116 .7 


120.2 


123.0 


127.8 


131-8 


134-8 137-S 


2 


77'.8 


88.9 


104.0 


no. 9 


116. 2 


120.3 


123 


8 


127 .0 


129 


9 


134-3 


138 





141. 143-3 


3 


82. 4 


93.7 


108.7 


II5-6 


120.8 


124.8 


128 


3 


131. 4 


134 


2 


138.6 


142 


3 


145.4 147-6 


4 


85.6 


97.0 


1 12 .0 


118. 9 


124.0 


128. I 


131 


5 


134.6 


137 


4 


141.9 


145 


S 


14S.6 


151-0 


5 


87.6 


99-3 


114. 4 


121. 3 


126. 5 


130.6 


134 


I 


137. 1 


140 





144-7 


148 


I 


151.2 


153.6 


6 


89.1 


lOI . 


116. 3 


123.2 


128.6 


132.6 


136 


3 


139.4 


142 


3 


140.9 


150 


S 


1S3-5 




7 


90 .0 


102.4 


118. 


125.0 


130.4 


134-6 


138 


2 


141 -5 


144 


5 


149.0 


152 


7 






8 


90 . 6 


I03-3 


119-3 


126.4 


132.0 


136.3 


140 





143-3 


146 


3 


151.0 


154 


9 






9 


90.7 


104. 


120.4 


127.7 


133.3 


137.7 


141 


6 


I45-0 


148 


1 


152.8 


156 


7 






lO 


90.8 


104. S 


121 .4 


128.8 


134.5 


139-0 


142 


9 


146.4 


149 


7 


154.6 








II 


90.9 


104.7 


122.0 


129.7 


135.6 


140. 2 


144 


2 


147-7 


151 













12 


91 .0 


104. 8 


122.5 


130.4 


136.4 


141 . I 


145 


2 


148.8 


152 


3 










13 


91 . 


105 .0 


122.9 


131 .0 


137. 1 


141.9 


146 


I 


149.8 


153 


2 










14 


91 .0 


105.0 


123. 2 


131.5 


137.6 


142.5 


146 


7 


150-5 


154 













IS 


91 .0 


105.0 


123.6 


131.8 


138.0 


142.9 


147 


2 


151-I 


154 


6 










20(?) 






123.9 


132.9 







































h=f-r ■ — . It is only necessary in a straight pipe or one nearly 

1 . h f v^ 

straight to compute the quantity s = j=-^ — . 

194. Timber-stave Pipes. — In the western part of the country 
long conduits or pipe-lines are frequently constructed of timber 
called redwood. Staves of suitable thickness, sometimes if 
inches, are accurately shaped and finished with smooth surfaces 
so as to form large pipes of any desired diameter. These staves 
are held rigidly in place with steel bands drawn tight with nuts 
on screw-ends, so as to close tightly the joints between them. 
Such wooden conduits are rapidly and cheaply built and are very 
durable. They have the further advantage of requiring no 
interior coating, as the timber surface remains indefinitely un- 
affected by the water flowing over it. The latter part of Table 
XV shows coefficients for Chezy's formula which may be used 
for such a class of timber conduits. As the interior surfaces of 
such closed conduits are always very smooth, the coefficients 
are seen to be relatively large, and such pipes are, therefore, well 
adapted to maintain imimpaired discharging capacity for great 
lengths of time. 



CHAPTER XVIII. 

195. Pumping and Pumps. — When it is impossible to secure 
water at sufficient elevation to be delivered to the points of con- 
sumption by gravity, it is necessary to resort to pumping in 
order to raise it to the desired level. Indeed it is sometimes 
necessary to resort to pumping in connection with a gravity 
supply in order to deliver water to the higher parts of the distri- 
bution system, the lower points being supplied by gravity. This 
combination of gravity supply with pumping is not unusual. 
That part of New York north of Thirty -fourth Street between 
Lexington and Fifth avenues, north of Thirty-fifth Street be- 
tween Fifth and Sixth avenues, north of Fifty-first Street be- 
tween Sixth and Ninth avenues, north of Fifty -fifth Street 
between Ninth and Tenth avenues, north of Fifty-eighth Street 
between Tenth and Eleventh avenues, and north of Seventy- 
second Street between Eleventh Avenue and the North River, 
with elevation of 60 feet or more above mean high tide- water, is 
supplied from the high-service reservoir near High Bridge, the 
water being elevated to it from the Croton supply by the pump- 
ing-station at the westerly end of the bridge. The elevation of 
the water surface in the High Bridge reservoir is 208 feet, and 
that of the large reservoir in Central Park 115 feet, above mean 
high tide-water. Some specially high points on the northern 
part of Manhattan Island are supplied from the High Bridge 
tower, whose water surface is 316 feet above mean high tide. 

The pumps employed for the purpose of elevating water to 
distributing-reservoirs are among the finest pieces of machinery 
built by engineers at the present time. They are usually actuated 
by steam as a motive power, the steam being supplied from suit- 
able boilers or batteries of boilers in which coal is generally used 
as fuel. The modern pumping-engine is in reality a combination 

254 



PUMPING AND PUMPS. 255 

of three classes of machinery, the boilers, the steam-engines, and 
the pumps. There are various types of boilers as well as of 
engines and pumps, all, when judiciously designed and arranged, 
well adapted to the pumping-engine process. The pumps are 




Skeleton Pumps. 

generally what are called displacement pumps ; that is, the w^ater 
in the pump-cylinder is displaced by the reciprocating motion 
of a piston or plunger. These pumps may be either double- 
acting or single-acting ; in the former case, as the piston or plunger 
moves in one direction it forces the water ahead of it into the 



256 WATER-WORKS FOR CITIES AND TOWNS. 

main or pipe leading up to the reservoir into which the water is 
to be delivered, while the water rising from the pump-well follows 
back of the piston or plunger to the end of its stroke. When 
the motion is reversed the latter water is forced on its way up- 
ward through the main, while the water rises from the pump-well 
into the other end of the water-cylinder. In the case of single- 
acting pumps water is drawn up into the water-cylinder from the 
pump-well during one stroke and forced up through the main 
during the next stroke, one operation only being performed at 
one time. The pump-well is a well or tank, usually of masonry, 
into which the water runs by gravity and from which the pump 
raises it to the reservoir. For the purposes of accessibility and 
convenience in repairing, the pump is always placed at an eleva- 
tion above the water in the pump-well, the pressure of the atmos- 
phere on the water in the well forcing the latter up into the 
pump-cylinder as the piston recedes in its stroke. The height 
of a column of water i square inch in section representing the 
pressure of the atmosphere per square inch is about 34 feet, but 
a pump-cylinder should not be placed more than about 18 feet 
above the surface of the water in the pump-well in order that 
the water may rise readily as it follows the stroke of the plunger. 

In the operation of the ordinary pump the direction of the 
water as it flows into and out of the pump-cylinder must neces- 
sarily be reversed, and this is true also with the type of pump 
called the differential plunger-pump, which is really a single-act- 
ing pump designed so as to act in driving the water into the main 
like a double-acting pump, i.e., both motions of the plunger force 
water through the main, but only one draws water from the 
pump-well into the pump-cylinder. Valves may be so arranged 
in the pump-piston as to make the progress of the water through 
the pump continuous in one direction and so avoid the irregu- 
larities and shocks which necessarily arise to some extent from a 
reversal of the motion of the water. 

The steam is used in the steam-cylinders of a pumping-engine 
precisely as in every other type of steam-engine. At the present 
time compound or triple-expansion engines are generally used, 
among the well-known types being theWorthington duplex direct- 
acting pump without crank or fly-wheel, the Gaskill crank and 



PUMPING AND PUMPS. 257 

fly-wheel pumping-engine, the Alhs and the Leavitt pumping- 
engines, both of the latter employing the crank and fly-wheel 
and both may be used as single- or double-acting pumps, usually 
as the latter. The characteristic feature of the well-known 
Worthington pumping-engine is the movement of the valves of 
each of the two engines by the other for the purpose of securing 
a quiet seating of the valves and smooth working. 

One of the most important details of the pumping-engine is 
the system of valves in the water-cylinder, and much ingenuity 
has been successfully expended in the design of proper valve 
systems. These pump-valves must, among other things, meet 
the following requirements as efficiently as possible: they must 
close promptly and tightly, so that no water may pass through 
them to create slip or leakage ; they should have a small lift, 
so as to allow prompt closing, and large waterways, to permit a 
free flow through them with little resistance ; they must also 
be easily operated, so as to require little power, and, like all details 
of machinery, they should be simple and easily accessible for 
repairing when necessary. 

As steam is always used expansively, its force impelling the 
plunger will have a constant value during the early portion of 
the stroke only, and a much less value, due to the expansion of 
the steam, at and near the end of the stroke, while the head of 
water against which the pump operates is practically constant. 
There is, therefore, an excess of effort during the first part of 
the stroke and a deficiency during the latter part. Unless there 
should be some means of taking up or cushioning this difference, 
the operation of the pump would be irregular during the stroke 
and productive of water-hammer or blows to the engine. Two 
means are employed to remove this undesirable effect, i.e., the 
fly-wheel and the air-chamber, or both. In the one case the 
excess of work performed by the steam in the early part of the 
stroke is stored up as energy in the accelerated motion of the 
fly-wheel and given out by the latter near the end of the stroke, 
thus producing the desired equalization. The air-chamber is a 
large reservoir containing air, attached to and freely communi- 
cating with the force main or pipe near its connection with the 
pumps. In this case the excess of work performed at the begin- 



258 



WATER-WORKS FOR CITIES AND TOWNS. 



ning of the stroke is used in compressing the air in the air-cham- 
ber, sufficient water entering to accomphsh that purpose. This 
compressed air acts as a cushion, expanding again at the end of 
the stroke and reinforcing the decreasing effort of the steam. 

196. Resistances of Pumps and Main — Dynamic Head. — Ob- 
viously the water flowing through the pipes, pump-cylinders, 
and pump-valves will experience some resistance, and it is one 
purpose in good pumping-engine design to make the progress of 
the water through the pump so direct and free as to reduce these 
losses to a minimum. Similarly the large pipe or main, called 
the force-main, leading from the pump up to the reservoir into 
which the water is delivered, sometimes several thousand feet 
long, will afford a resistance of friction to the water flowing 
through it. The head which measures this frictional loss is given 
by equation (10) on page 239. All these resistances will increase 




Allis Pump. 

rapidly with the velocity with which the water flows through 
the pipes and other passages, as do all hydraulic losses. It is 
obviously advisable, therefore, to make this velocity as low as 
practicable without unduly increasing the diameter of the force- 
main. This velocity seldom exceeds about 3 feet per second. 



RESISTANCES OF PUMPS AND MAIN. 



259 




Section of Allis Pumping Engine. 



260 WATER-WORKS FOR CITIES AND TOWNS. 

The static head against which the pumping-engine operates 
is the vertical height or elevation between the water surfaces 
in the pump-well and the reservoir. The head which represents 
the resistances of the passages through the pump and force-main, 
when added to the sum of the static head and the head due to 
the velocity in the force-main, gives what is called the dynamic 
head; it represents the total head against which the pump acts. 
If h represents the static head, h^ the head due to all the resist- 
ances, and JV' the head due to the velocity in the force-main, 

then the dynamic head will heH =h-{- h' + h" =h-\-H — + n \ , 

in which / has a value of about .015 and 11 is a coefficient which 
when multiplied by the velocity head will represent the loss of 
head incurred by the water in passing through the pump-cylinder 
and valves. The latter quantity is variable in value ; but it is 
seldom more than a few feet. 

197. Duty of Pumping-engines. — It is thus seen that the col- 
lective machines and force-main forming the pumping system 
afford opportunity for a number of serious losses of energy found 
chiefly in the boiler, the engine, and the pump. The excellence 
of a pumping-plant, including the boilers, may obviously be 
measured by the amount of useful work performed by a standard 
quantity, as 100 pounds of coal. Sixty or more years ago, in 
the days of the old Cornish pumping-engine, the standard of 
excellence or ' ' duty ' ' was the number of foot-pounds of work, 
i.e., the number of pounds lifted one foot high, performed by one 
bushel of coal. As early as 1843 the Cornish pumping-engine 
reached a duty, per bushel of coal, of 107,500,000 foot-pounds. 
These pumping-engines were single-acting, the steam raising a 
weight the descent of which forced the water up the delivery- 
pipe. 

At a later date and until about ten years ago the usual stand- 
ard or criterion applied to pumping-engines for city water-works 
was the amount of work performed in lifting water for each 100 
pounds of coal consumed ; this result was also called the ' ' duty ' ' 
of the engine. In order to determxine the duty of a pumping- 
engine it was thus only necessary to observe carefully for a given 
period of time, i.e., twenty-four hours or some other arbitrary 



DATA TO BE OBSERVED IN PUMPIXG-ENGINE TESTS. 2G1 

period, the amount of coal consumed, the condition of the furnace- 
fires at the beginning and end of the test being as nearly the 
same as possible, and measure at the same time the total amount 
of water discharged into the reservoir. The total weight of 
water raised multiplied by the total number of feet of elevation 
from the water surface in the pump-well to that in the reservoir 
would give the total number of foot-pounds of useful work per- 
formed. This quantity divided by the number of hundred 
pounds of coal consumed would then give what is called the 
"duty" of the pumping-engine. 

198. Data to be Observed in Pumping-engine Tests. — Ob- 
viously it is necessary to observe a considerable number of data 
with care. No pump works with absolute perfection. A little 
water will run back through the valves before they are seated, 
and there will be a little leakage either through the valves or 
through the packing around the piston or plunger, or both sources 
of leakage may exist. That leakage and back-flow represent the 
amount of slip or water which escapes to the back of the plunger 
after having been in front of it. In well-constructed machinery 
this slip or leakage is now very small and may be but a smiall 
fraction of one per cent. Inasmuch as the amount of work per- 
formed by the steam will be the same whether this slip or leakage 
exists or not, the latter is now frequently ignored in estimating 
the duty of pumping-engines, the displacement of the piston or 
plunger itself being taken as the volume of water pumped at 
each stroke. 

Again, in discussing the efficiency of the steam portion of the 
machinery the amount of partial vacuum maintained in the 
vacuum-pump, which is used to move the water of the condensed 
steam, is affected by atmospheric pressure, as is the work which 
is performed. Hence in complete engine tests it is necessar}^ 
to observe the height of the barometer during the test. It is also 
necessary to observe the temperature of feed-water supplied to 
the boiler, and to use accurate appliances for ascertaining with 
the greatest exactness practicable the weight of dr}- steam used 
in the steam-cylinders and the amount of water which it carries. 
It is not necessar}^ for the present purpose to discuss wdth minute- 
ness these details, but it is evident from the preceding obser^^a- 



263 WATER-WORKS FOR CITIES AND TOWNS. 

tions that the complete test of a pumping-engine involves the 
accurate observation of many data and their careful use in com- 
putations. The determination of the duty alone is but a simple 
part of those computations, and the duty is ah that is now in 
question. 

199. Basis of Computations for Duty. — It was formerly neces- 
sary in giving the duty of a pumping-engine to state whether 
the 100 pounds of coal was actually coal as shovelled into the 
furnace, or whether it was that coal less the weight of ash remain- 
ing after combustion. It was also necessary to specify the quaHty 
of coal used, because the heating capacity of different coals may 
vary materially. For these different reasons the statement of 
the duty of a pumping-engine in terms of a given weight of coal 
consumed involved considerable uncertainty, hence in 1891 a 
committee of the American Society of Mechanical Engineers, 
appointed for the purpose, took into consideration the best 
method of determining and stating the duty of a pumping- 
engine. The report of that committee may be found in vol. xii 
of the Transactions of that Society. The committee recom- 
mended that in a duty test 1,000,000 heat-units (called British 
Thermal Units or, as abbreviated, frequently B.T.U.) should be 
substituted for 100 pounds of coal. In other words, that the 
following should be the expression for the duty : 

_ foot-pounds of work done 

total number of heat-units consumed ' 

For some grades of coal in which 1,000,000 heat-units would 
be available for every 100 pounds the numerical value of the duty 
expressed in the new terms would be unchanged, but for other 
grades of coal the new expression of the duty might be consid- 
erably different. 

200. Heat-units and Ash in 100 Pounds of Coal, and Amount 
of Work Equivalent to a Heat-unit. — The following table exhibits 
results determined by Mr. George H. Barrus (Trans. A. S. M. E., 
vol. xrv. page 816), giving an approximate idea of the total num- 
ber of heat-units which are made available by the combustion of 
1 00 pounds of coal of the kinds indicated : 



HEAT-UNITS AND ASH. 203 

Semibituminous : 

George's Creek Cumberland, Percentage of Ash. 

1,287,400 to 1, 421, 700 6.1 to 8.6 

Pocahontas, 

1,360,800 to 1,460,300 3 . 2 to 6 . 2 

New River, 

1,385,800 to 1,392,200 3-5 to 5.7 

Bituminous : 

Youghiogheny, Pa., lump, 

1,294,100 5.9 

Youghiogheny, Pa., slack, 

1,166,400 10.2 

Frontenac, Kan., 

1,050,600 17.7 

Cape Breton Caledonia, 

1,242,000 8.7 

Anthracite : 

1,152,100 to 1,318,900 9.1 to 10. 5 




Wnrthiiigtcin Pump. 



2G4 



WATER-WORKS FOR CITIES AND TOWNS. 



Each unit or B.T.U. represents the amount of heat required 
to raise one pound of water at 32° Fahr. 1° Fahr., and it is equal 
to 778 foot-pounds of work. In other words, 778 foot-pounds of 
work is said to be the mechanical equivalent of one heat-unit. The 
amount of work, therefore, which one pound of dry steam is cap- 
able of performing at any given pressure and at the corresponding 
temperature may readily be found by multiplying the number of 
available heat-units which it contains, and which may be readily 




Section of Worthington Pump. 

computed if not already known, by 778, or as in a pumping- 
engine duty trial, knowing by observation the number of pounds 
of steam at a given pressure and temperature supplied through 
the steam-cylinders, the number of heat-units supplied in that 
steam is at once known or may easily be computed. Then 
observing or computing the total weight of water raised by the 
pumping-engine, as well as the total head (the dynamic head) 
against which the pumping-engine has worked, the total num- 
ber of foot-pounds of work performed can be at once deduced. 
This latter quantity divided by the number of million heat-units 
will give the desired duty. 



THREE METHODS OF ESTIMATING DUTY. 265 

201. Three Methods of Estimating Duty. — At the present 
time it is frequently, and perhaps usually, customary to give the 
duty in terms of loo pounds of coal consumed, as well as in terms 
of 1,000,000 heat-units. Frequently, also, the duty is expressed 
in terms of 1000 pounds of dry steam containing about 1,000,000 
heat-units. As has sometimes been written, the duty unit is 
100 for coal, 1000 for steam, and 1,000,000 for heat-units. 

202. Trial Test and Duty of AUis Pumping-engine. — The fol- 
lowing data are taken from a duty test of an Allis pumping-engine 
at Hackensack, N. J., in 1899 by Prof. James E. Denton. This 
pumping-engine was built to give a duty not less than 145,000,000 
foot-pounds for each " 1000 pounds of dry steam consumed by 
the engine, assuming the weight of water delivered to be that of 
the number of cubic feet displaced by the plungers on their in- 
ward stroke, i.e., to be 145,000,000 foot-pounds at a steam 
pressure of 175 pounds gauge." The capacity of the engine was 
to be 12,000,000 gallons per twenty-four hours at a piston speed 
not exceeding 217 feet per minute. The engine was of the verti- 
cal triple -expansion type with cylinders 25.5 inches, 47 inches, 
and 73 inches in diameter with a stroke of 42 Jg inches, the single- 
acting plunger being 25.524 inches in diameter. The following 
data and figures illustrate the manner of computing the duty : 

DUTY PER 1000 POUNDS OF DRY STEAM BY PLUNGER DISPLACEMENT. 

1. Circumference of plungers, CI 80 . 1875 ins. 

2. Length of stroke, 7 42 .0625 ins. 

3. Number of plungers (single-acting) 3 

4. Aggregate displacement of plunger per revolution = 

■2CV 
—^ =d 64,4557 ■ I cu. ins. 

5. Revolutions during 24 hours, A" 43.337 

6. Weight of one cubic foot of water, w 62.42 lbs. 

Total head pumped against, H 266 .61 ft. 

Total feed- water per 24 hours, W 160,354 lbs. 

r^ .- ^v. f ( A ^ J^w HxNXiooo 

Duty per 1000 lbs, of teed- water = X^ tjt- 

1728 ^•^^ 

266 . 61 X4'^, 3^7 X 1000 ,„ r, ,., 

= 2 ^:!i,g76X Ci^^'APJ-1 = 168,027,200 ft. -lbs, 

160,354 

Percentage of moisture in steam at engine-throttle 

valve 0.3 per cent. 

Duty per 1000 lbs. of dry steam, ' '- = 168,532,800 ft. -lbs. 

-' ^ -^ 0-997 



266 



WATER-WORKS FOR CITIES- AND TOWNS. 



DUTY PER MILLION HEAT-UNITS. 

12. Average steam pressure at throttle above atmosphere. 173 lbs. 

13. Average feed- water temperature 78° • 5 Fahr. 

14. Total heat in one pound of steam containing 0.3 per 

cent, of moisture above 32° Fahr 1,194.2 B. T. U. 

15. Heat per lb. of feed- water above 32° Fahr 46.5 

16. Heat supplied per lb. of feed- water above 32° Fahr i,i47-7 

17. Duty per lb. of feed-water 168,027 . 2 ft. -lbs. 

18. Duty per miUion B. T. U 146,403,614 

203. Conditions Affecting Duty of Pumping-engines. — Mani- 
festly the duty of a pumping-engine by whatever standard it may 
be measured will vary with the conditions under which it is made. 
A new engine running under the favoring circumstances of a 
short-time test may be expected to give a higher duty than when 
running under the ordinary conditions of usage one month after 
another. Hence it can scarcely be expected that the monthly 
performance, and much less the yearly performance, of an engine 
will show as high results as when tested for a day or two or for 
less time. 

204. Speeds and Duties of Modern Pumping-engines. — The 
following table gives the piston or plunger speeds of a number of 
the best modern pumping-engines, and the corresponding duties, 
with the standards by which those duties are measured. 



Engine. 



Ridgewood Station, Brooklyn, 
Worthington engine 

14th St. pumping- station, 
Chicago ; built by Lake Erie 
Engine Works 

AUis engine at Hackensack, 
N.J 

Snow pump at Indianapolis . . . 

Leavitt pump at Chestnut Hill 

Nordberg at Wildwood 

AUis at Chestnut Hill, tested 
May I, 1900 

Allis at St. Louis, tested Feb- 
ruary 26, 1900 

Barr at Waltham, Mass 

Allis at St. Paul, Minn 

Lake Erie Engine Works at 
Buffalo 



Piston speed 

in Feet 
per Minute. 



164 .0 



210.54 

210.65 
214.6 



256.0 

192.5 

197.16 
194. a 8 
189 .0 

207.7 



Duty in Foot- 
pounds. 



137.953.585 



133.445.000 

146,403,416 
150,100,000 
144,499,032 
162,132,517 

157.002,500 

158,077,324 
128,865,000 
144,463,000 

135.403,745 



Expressed in 



1 000 lbs. of dry steam 



Minion B. T. U. 



MiUion B. T. U. 
1000 lbs. of dry steam 
Million B. T. U. 



These results show that material advances have been made 
in pumping-engine designs within a comparatively few years. 



CHAPTER XIX. 

205. Distributing-reservoirs and their Capacities. — The water of 
a public supply seldom runs from the storage-reservoir directly 
into the distributing system or is pumped directly into it, al- 
though such practices may in some cases be permissible for small 
towns or cities. Generally distributing-reservoirs are provided 
either in or immediately adjacent to the distributing system of 
pipes, meaning the water-pipes large and small which are laid 
through the streets of a city or town, and the service-pipes lead- 
nig from the latter directly to the consumers. 

The capacity ordinarily given to these distributing-reservoirs 
is not controlled by any rigid rule, but depends upon the local 
circumstances of each case. If they are of masonry and covered 
with masonry arches, as required for the reception of some filtered 
waters, they are made as small as practicable on account of their 
costs. If, on the contrary, they are open and formed of suitably 
constructed embankments, like the distributing-reservoirs of 
New York City in Central Park and at High Bridge, they are and 
should be of much greater capacity. The storage volume of the 
High Bridge reservoir amounts to 11,000,000 gallons, while that 
of the Central Park reservoir is 1,000,000,000 gallons. Again, 
the capacity of the old receiving-basin in Central Park is 
200,000,000 gallons. These reservoirs act also as equalizers 
against the varying draft on the system during the different por- 
tions of the day and furnish all desired storage for the demands 
of fire-streams, which, while it lasts, may be a demand at a high 
rate. It may be approximately stated under ordinary circum- 
stances that the capacity of distributing-reservoirs for a given 
system should equal from two or three to eight or ten days' 

267 



268 WATER-WORKS FOR CITIES AND TOWNS. 

supply. It is advantageous to approach the upper of those 
Hmits when practicable. The volume of water retained in these 
reservoirs acts in some cases as a needed storage, while repairs 
of pumping-machinery or other exigencies may temporarily stop 
the flow into them. The larger their capacity the more effec- 
tively will such exigencies be met. 

206. System of Distributing Mains and Pipes. — Gate-houses 
must be placed at the distributing-reservoirs within which are 
found and operated the requisite gates controlling the supply into 
the reservoir and the outflow from it into the distributing system. 
The latter begins at the distributing-reservoir where there rnay 
be one or two or more large mains, usually of cast iron. These 
mains conduct the water into the branching system of pipes which 
forms a network over the entire city or town. A few lines of large 
pipes are laid so as to divide the total area to be supplied into 
convenient portions served by pipes of smaller diameter leading 
from the larger, so that practically every street shall carry its 
line or lines of piping from which every resident or user may 
draw the desired supply. Obviously, as a rule, the further the 
beginning of the distributing system is departed from in follow- 
ing out the ramifications of the various lines the smaller will the 
diameter of pipe become. The smallest cast-iron pipe of a dis- 
tributing system is seldom less than 3 inches, and sometimes not 
less than 4 or 6 inches. There should be no dead ends in any 
distributing system. By a dead end is meant the end of a line of 
pipes, which is closed so that no water circulates through it. 
Whenever a branch pipe ceases it should be extended so as to 
connect with some other pipe in the system in order to induce cir- 
culation. The entire distributing system should therefore, in 
its extreme as well as central portions, constitute an interlaced 
system and not a series of closed ends. This is essential for the 
purity and potability of the water-supply. A circulation in all 
parts of the entire system is essential and it should be everywhere 
secured. 

The diagram shows a portion of the distributing system of 
the city of New York. It will be noticed that there is a com- 
plete connection of the outlying portions, so as to make the inter- 









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NO .tl3 

CISTRIBUTION PIPES OF THt 

PUBLIC WATER. 

SUPPLY OF THE CITY OF MEW YORK 

BOROUGH OF MANHATTAN 

Gompilcd (r,m PI jn, h, QfCte W Iho 

CHIEF ENGINEER OF OEPT--OF WATER SXlPPUY 

e, E. D PIngiee, M. E. 

^«d*i Sufwrviatoo of John R. Freeman. C.E. 

October, 1639 Scslt. 1 -inch J «J f„l. 



»,«ni.ovT amsW"^ 



^—Hl — 



tributing System. 




NO 113 
DISTRIBUTION PIPES OF THE 

PUBLIC WATER. 

SUPPLY OF THE CITy OF NEW YORK 

BOROUGH OF MANHATTAN 



Fin. 4.— New York City Distributing Systen 



DISTRIBUTING MAINS AND PIPES. 



269 



lacing and corresponding circulation as complete and active as 
possible. 

207. Diameters of and Velocities in Distributing Mains and Pipes. 

— In laying out a distributing system it will not be possible 
to base the diameters at different points on close computations 
for velocity or discharges based upon considerations of friction 
or other resistances, as the conditions under which the pipes are 
found are too complicated to make such a method workable. 
Approximate estimates may be made as to the number of con- 
sumers to be supplied at a given section of a main pipe, and con- 
sequently what the diameter should be to pass the required daily 
supply so that the velocity may not exceed certain maximum 
limits known to be advisable. Such estimates may be made 
at a considerable number of what may be termed critical points 
of the system, and the diameters may be ascertained in that man- 
ner with sufficient accuracy. In this field of hydraulics a sound 
engineering judgment, based upon experience, is a very important 
element, as it is in a great many other engineering operations. 

It will follow from these considerations that as a rule the 
larger diameters of pipe in a given distributing system will belong 
to the greater lengths, and it will be found that the velocities of 
water in the various parts of a system will seldom exceed the 
following limits, which, although stated with some precision, are 
to be regarded only as approximate : 



For 4-inch pipe 23 feet per second. 



6 
8 
1 1 
12 
16 
20 
24 

30 
36 
48 
60 



23 
17 
12 
12 

9 

8 

7 
7 
7 
7 
7 



270 WATER-WORKS FOR CITIES AND TOWNS. 

208. Required Pressures in Mains and Pipes. — In designing 
distributing systems it is very essential so to apportion the pipes 
as to secure the requisite pressure at the various street services. 
Like many other features of a water-supply system no exact 
rules can be given, but it may be stated that at the street-level a 
pressure of at least 20 to 30 pounds should be found in resident 
districts, and from 30 to 35 or 40 pounds in business districts. 
The character and height of buildings affect these pressures to 
a large extent. Old pipe systems usually have many weak 
points, and while pressures requisite to carry water to the top of 
three- or four-story buildings are needed, any great excess above 
that would be apt to cause breaks and result in serious leakages. 
If the distributing system is one in which the pressure for fire- 
streams is to be found at the hydrants, then greater pressures than 
those named must be provided. In such cases the pressures in 
pipes at the hydrants should range from 60 to 100 pounds. 

209. Fire-hydrants. — Fire-hydrants must be placed usually 
at street corners, if the blocks are not too long, and so distributed 
as to control with facility the entire district in which they are 
found. Unless fire-engines are used to create their own pressure, 
the lower the pressure at the hydrant the nearer together the 
hydrants must be placed. It is obvious, however, that when the 
pressure of the system is depended upon for fire-streams it is 
desirable to have the pressure comparatively high, so far as the 
hydrants are concerned, as under those conditions they may be 
placed farther apart and a less number will be required. 

210. Elements of Distributing Systems. — The following table 
gives a number of statistics, exhibiting the elements of the dis- 
tributing system of a considerable number of cities, including some 
pumping and meter data pertinent to the costs of pumping on 
the one hand and the extension of the use of meters on the other. 

It contains information of no little practical value in connec- 
tion with the administration of the distributing systems and the 
consumption of water in it. This table has been compiled by 
Mr. Chas. W. Sherman of the New England Water-works Asso- 
ciation, and was published in the proceedings of that association 
for September, 1901. The service-pipes, varying from ^ to 10 



ELEMENTS OF DISTRIBUTING SYSTEM. 271 

inches in diameter, are of cast iron, wrought iron, lead, galvanized 
iron, tin-lined, rubber-Hned, cement-lined, enamelled and tarred, 
the practice varying widely not only from one city to another, 
but in the same city. 



272 



WATER-WORKS FOR CITIES AND TOWNS. 



TABLE 



Name of City or Town. 



1^ 






Albany, N. Y 

Atlantic City, N. J. 
Boston, Mass 



Burlington, Vt. . . 

Cambridge, Mass 
Chelsea, Mass. . . . 



Concord, N. H . . . 
Fall River, Mass. . 
Fitchburg, Mass. . 

Holyoke, Mass . . . 

Lowell, Mass 

Lynn, Mass 

Madison, Wis 

Manchester, N. H. 



Metropolitan 
Water-works 



j Owned by. 



Tot. Sup. by. 



C.L 

C.L 
C.L. 
C.L 
W.L 



C.I. 
(CI. 
■( C.L, 

C.L 

C.L 

jC.L 
/W.L 



Minneapolis, Minn... 
New Bedford, Mass. 
New London, Conn . 

Newton, Mass 

Providence, R. I.. . . 



H.P. Fire System . 



Quincy, Mass 



Springfield, Mass . 

Woonsocket, R. I. 
Yonkers, N. Y , . . 



Worcester, Mass . 



(W.L 

■<C.L. 

(C.L 
C.L 

(C.L. 

1 C.L 

I C.L 

ICL. 

I C.L 

•^C.L. 

(Kal. 

JC.L 

( Steel. 
C.L 
W.L 
C.L. 
C.L 
C.L 

C.L 

C.L 

(W.L 

(C.L. 

jC.L 

(Kal. 

C.L 



4-30 



6-16 
4-30 
6-24 
2-20 

4-30 



2-20 

4-16 
4-20 
6-60 

4-60 

ii-50 
4-36 
4-24 
4-20 
6-36 

1 2-24 
1-36 

2-20 
4-20 



129.7 
47.6 

713.4 
38.0 



37.8 
60 . 2 
87.3 
66.6 

81.6 
127.8 

129.4 

34-3 
96.9 

69.8 
1360.3 

269 . 2 
92.7 

SO -5 

136.6 

324.6 

5-6 

144-7 

84. 1 

45.8 
74-1 



27 .09 
4. 61 



24. 00 

18.71 

6.43 

0.56 



519 
7606 

213 

968 
253 
267 
954 
499 
860 
1098 

952 
169 

743 



3172 
738 

258 

935 

1886 

92 

955* 

539 

548 
771 

1763 



Public hydrants only. 



ELEMENTS OF DISTRIBUTING SYSTEM. 



273 



XIX. 





Range of Pressure on 
Mains at Centre, 
Pounds. 


0) 

n 
'5, 
0!) 

> w 

o>-i 


Total Number of 
Service-taps in 
Use. 


6 
•E.S 

¥ 


Cn>^ ■ 

" 


Average Static Head 
against which 
Pumps Work, 
Feet. 


803 








2030 
3298 
4516 

2311 

860 
104 

lOIO 

6,544 
2.427 

210 
5,586 

2,571 

2.586 

3,667 

10,385 










i-4 

i-8 

i-6 


4,249 

87,525 

3,350 

14,207 
6,146 

3,340 

6,943 

4,432 

3,610 

10,634 

13,504 

2,758 

5,513 

134,496 


1 955,726,046 
1 148,662,947 


81.7 




40-90 
70-85 


119. 5 


618 


312,896,525 
2,651,277 240 


289 


309 

757 
940 

554 

734 
1188 


48-50 


1-2 




142,772,165 
1,388.776,336 




80 
i 75 L.S. 
(I5SH.S. 

80-100 


*-2 

i-8 

f-4 


186.2 






2,042,066.140 

378,782,675 
1,330,784.875 

306,637,454 


156. 1 




45-6c 


i-4 




066 




234 


223.8 




■ i-6 


268 




15,027,410,000(0) 

9,431,140,000(6) 
2, 015, 130, 000(c) 

6,863,135,200 
2,307 429,372 
























219s 




■J- 10 
i-4 
i-6 
i-io 


20,064 
9,280 

3,088 

7,087 

21,566 


5,030 

1.429 

229 

6,001 

17,813 




1065 
318 
801 

3399 
31 


28-64 
40-4S 

84 
64-73 

114 

J 30-35 H.S. 
( loo-i 20 L.S.* 

78-85 
50-1 20 


167.2 


762,876,073 

3,833,243,445 

34,401,038 

578,940,480 


234 

171 . 6 
172.4 


1-6 

1-3 
1-6 

-i-8 


9,764 

4,330 

2,193 
4,968 

13,292 


3,122 

122 

1,889 
4,852 

12,529 








456 
498 


340,849,628 
1,323,696,099 


237.6 


2432 


j 70 L.S. 
I1S0H.S.* 













274 



WATER-WORKS FOR CITIES AND TOWNS. 



TABLE 



Name of City or Town • 


Kind of Pipe. 


6 

ft 

o 

0) 
N 


Average Dynamic 
Head against which 
Pumps Work, 
Feet. 


Duty in Foot-pounds 
per 100 Pounds of 
Coal. No Deduc- 
tions. 


Albany N. Y 










Atlantic City N. T 


C.I. 

C.I. 
( C.L. 

C.I. 
( W.I. 


4-20 

2-48 
4-30 


j 123-3 
1 iiQ-S 


36,501,217 




15,518,455 




316 




Cambridcre Miss 






C.I. 
iCI 
1 C.L. 

C.I. 

C.I. 

(C.I. 
"( W.I. 


6-16 
4-30 

6-24 
2-20 

i-30 






Concord N. H 






Fall River, Mass 


















Lowell, Mass 


163.9 

( 167 
"( 167 

242.4 


93,489,048 
88,780,036 




i W.I. 
^C.L. 

(c.i. 

C.I. 
(C.L. 

1c.i. 

J C.I. 
IC.L 
^C.I. 
i C.L. 

Kal. 
(CI. 
1 Steel. 

C.I. 
I W.I. 
^C.L. 
(C.L 

C.I. 

C.I. 

C.I. 
(C.I. 
1 Kal. 
I W.I. 
^C.I. 
(C.L. 

C.I. 


2-20 

4-16 
4-20 

6-60 

4-60 

i4-So 
4-36 
4-24 
4-20 
6-36 

12-24 
2-20 

1-35 
4-20 




87,265,319 
47,530,839 


Manchester, N. H 


Owned by 

Metropolitan 1 

Water-works j Tot. Sup. by... . 


96-5 

(51.8 
I12S.6 

192 


121,800,000 

109,380,000 
80,400,000 

68,016,609 
130,336,508 




New London, Conn 




254 
( 176.9 
) 177-7 
( 124.7 






101,301,600 
69,329,100 
68,533,300 


H.P. Fire-system. . .... 


Quincy, Mass 






Springfield, Mass 








239. 5 


51,024,641 


Yonkers N Y 






2-40 















ELEMENTS OF DISTRIBUTING SYSTEM. 



275 



XIX. — Continued. 



(S o C c 

O o o 3 



3 '-' u ^ 

u, f ■ S. C 



o 






0.0399 

0.042 

0.159 



0.0314 

0.032 

0.043 



0.033 
0.0259 



c <" ,^ • 



$0 . 264 



0.366 



o. 2867 



0.59 

L.S. = . 0259 
H.S. = o. 1134 



$916,723.59 

23,054.387.81 

468,039.73 

5,670,229.52 
483,335-52 
857,440.98 

1,937,862.93 
452,091 .09 

1,244,742.23 



2,472,821 . 8s 

337,630.13 

1,513,012. 79 



1,820,107 . 73 
706,978.44 



■2,034,808 .07 
6,470,093.3s 



2,128,559.56 

390,841.78 
1,577,105.15 



■d <A 



$892,000 

11,960,272 

248,000 

3,302,100 
300,000 

650,000 

1,920,000 

648,000 

300,000 

1,274,700 



550,000 
410,000 



2,075,000 
5,920,000 



720,500 
1 ,500,000 



$100,407 .01 

10,144,647 .08 

64,076 .40 

604,326.58 
50,921 

581,647.78 
195,908.91 

37,403.46 
287,226. 20 
524,027.50 

159,466.83 



849,115.40 
713,431.62 



461,861 . 90 
310,700 



42-S 
32-6 

32-4 
4 
S.I 



4-6 



av. 4.44 
3-5-4 



av. 4.7 
av. 3.7 



4 

av. 5 . 9 



C.L. = cement-lined, 
(a) = Chestnut Hill high service. 
(&) = Chestnut Hill low service, 
(c) = Spot Pond Pumping-station. 



CHAPTER XX. 

211. Sanitary Improvement of Public Water-supplies. — In 

the preceding consideration of a public water-supply it has been 
virtually assumed that the water will reach consumers in the 
proper sanitary condition ; but this is not always the case. With 
great increase of population and corresponding increase of manu- 
facturing and other industries there arise many sources of con- 
tamination, so that pure spring- or river-water for public supplies 
becomes less available and at the present time in this country it 
is rarely to be had. 

The legal responsibility of parties who allow sewage, manu- 
facturing wastes, or other contaminating matter to flow into 
streams is already clearly recognized, and many cities and towns 
are required to dispose of their sewage and other wastes in such 
manner as to avoid polluting streams of water flowing past sewer 
outfalls or manufacturing establishments; but even these re- 
straints are not sufficient. If a stream has once been polluted 
it can scarcely be considered safe as a supply for potable water 
for public or private purposes. There are certain diseases 
whose bacilli are water-borne and which are conveyed by 
drinking-water containing them ; prominent among such diseases 
are typhoid fever and cholera. Experience has many times 
shown that these bacilli or disease germs may find their way 
from isolated country houses as well as from the sewage of 
cities into water that would otherwise be potable. Besides such 
considerations as these it is equally well known from engineering 
experience that many waters of otherwise fair quality carry the 
remains of organic matter in one shape or another which operate 
prejudicially to the physical condition of those who drink such 
water. It is therefore becoming more and more the conviction 
of civil engineers and sanitarians that there are few sources of 

276 



IMPROVEMENT BY SEDIMENTATION. 277 

potable water so free from some degree of pollution that the 
sappHes drawn from them do not require treatment in order to 
put them into good condition for drinking. It is not intended 
in this observation to state that there are no streams or springs 
from which natural waters may not be immediately used for 
domestic purposes without improving them by artificial means 
but it may be stated even at the present tim.e that no water of a 
public water-supply should be used without treatm.ent, unless 
the most thorough bacteriological examinations show that its 
sanitary condition is eminently satisfactory. 

It is the common experience of many public water-supplies 
in this country that during certain seasons of the year, extending 
through the summer and autumn months, certain low forms of 
vegetation flourish, causing sometimes discoloration and always 
offensive tastes and odors. While such waters are usually not 
dangerous, they certainly are not desirable and may cause the 
human system to become receptive in respect to pathogenic 
bacilli. The tendency at the present time, therefore, is to con- 
sider the improvement of any water-supply that may be con- 
templated for any city or town. 

212. Improvement by Sedimentation. — The two broad methods 
of improving the water of a public supply at the present time are 
sedimentation and filtration, the latter generally through clean 
sand, although sometimes other fine granular material or porous 
mass is used. The operation of sedimentation is carried on when 
water is allowed to stand absolutely at rest or to move through a 
series of basins with such small velocity that the greater portion 
of the solid material held in suspension is given an opportunity 
to settle to the bottom. All water which is taken from natural 
sources, whether surface or underground, carries some solid 
matter. Some waters, like spring- water or from an underground 
supply, are so clear as to be very nearly free from solid matter 
in suspension, but, on the other hand, there are waters, like those 
from silt-bearing rivers, which carry large amounts. Observa- 
tions upon the Mississippi River at St. Louis have shown that the 
suspended matter may reach as much as looo parts in one million, 
although the quantity held in suspension is usually much less 
than that. Similar observations have been made upon other 



278 WATER-WORKS FOR CITIES AND TOWNS. 

silt-bearing streams. Such large proportions of suspended solid 
matter are not usually found m streams used for potable pur- 
poses, but there are few surface sources of water-supply the water 
from which will not be sensibly improved by sedimentation in 
settling-basins or reservoirs. 

The process of sedimentation is usually preliminary to that 
of filtration. If raw water, i.e., as it comes from its natural 
source, is conducted directly to filtration-beds, the amount of 
solid matter is frequently so great that the surface of the filter 
would be too quickly clogged ; hence it is advisable in almost every 
case to subject to sedimentation any water which is designed 
to be treated subsequently by filtration. 

The degree of turbidity is usually measured by means similar 
to those employed in gauging discoloration from vegetable matter. 
One method devised by Mr. Allen Hazen, to which allusion will 
again be made, is that in which the depth in inches is observed 
at which a platinum wire i mm. in diameter and i inch long can 
be seen. The degree of turbidity is then represented by the 
reciprocal of that distance. The permissible turbidity estimated 
in this manner is taken by different authorities at different values 
running from .025 to .2. Water of this degree of turbidity 
appears, when seen through a glass, to be practically clear. 

The rapidity with which sedimentation can be performed 
depends greatly upon the character and degree of comminution 
of the solid material. If it is coarse, comparatively speaking, 
it will quickly fall to the bottom; if the solid matter is clay of 
fine texture, it is dissipated through the water in an excessively 
high degree of diffusion and will remain obstinately suspended. 
This has been found to be the case at some points with the Ohio 
River water. Ordinarily sufficient sedimentation can be accom- 
plished where the water remains at rest from twenty-four to 
forty-eight hours; in general, observations as to this matter, 
however, must be applied very cautiously . Water of the Missis- 
sippi River at St. Louis has been found to deposit nearly all of 
its sediment within twenty-four hours. At Cincinnati, on the 
other hand, the Ohio River water carries so fine a sediment that 
on an average not more than 75 per cent of it will be deposited 
in three days by unaided subsidence. Again, at Omaha the 



SEDIMENTATION AIDED BY CHEMICALS. 279 

water of the Missouri River has been found to be turbid at the 
end of seventy-two hours. In some cases, as with the waters 
of the Delaware and Schuylkih at Philadelphia, a greater amount 
of subsidence has been tound to exist at times at the end of 
twenty-four hours than after forty-eight hours. It is obvious 
that some special conditions must have produced such results 
that would not ordinarily occur in connection with the operation 
of sedimentation. 

213. Sedimentation Aided by Chemicals. — In cases where sim- 
ple unaided subsidence proceeds too slowly it can be accelerated 
by the introduction of suitable chemicals. At Cincinnati, for 
instance, it was found advantageous to introduce into the water 
before flowing into the settling-basins a small amount of alum 
or sulphate of alumina, depending upon the degree of turbidity, 
the average being about 1.6 grains per gallon, rising to perhaps 
4 grains in floods. By these means a few hours of aided sedi- 
mentation would produce more subsidence than could be ob- 
tained in several days without the chemicals. A similar recom- 
mendation has been made for the purpose of improving the water- 
supply for the city of Washington, D. C, from the Potomac 
River. In other cases between 5 and 6 grains of lime per gallon 
have produced effective results. 

214. Amount of Solid Matter Removed by Sedimentation. — - 
Under adverse conditions, or with sediment which remains obsti- 
nately suspended, not more than 25 to 50 per cent of the solid 
material will be removed by sedimentation, but when the process 
is working satisfactorily, sometimes by the aid of chemicals 
acting as coagulants, 90 to 99 per cent even of the solid material 
may be removed. The operation of sedimentation has another 
beneficial effect in that the solid matter when being deposited 
carries down with it large numbers of bacteria, which, in some 
cases, have been observed to be 80 or 90 per cent of the total 
contents of the water. In other words, the subsidence of the 
solid matter clears the water of a large portion of the bacteria. 

215. Two Methods of Operating Sedimentation-basins. — Sedi- 
mentation is carried on in two ways, one being the "fill-and- 
draw" method and the other the "continuous" method. In 
the former method a basin or reservoir is first filled with water 



280 WATER-WORKS FOR CITIES AND TOWNS. 

and then allowed to stand while the subsidence goes on for per- 
haps twenty-four hours. The clear water is then drawn off, 
after which the reservoir is again filled. In the continuous 
method, on the other hand, water is allowed to flow into a single 
reservoir or series of reservoirs through which it passes at an 
extremely low velocity, so that its contents will not entirely 
change within perhaps twenty-four hours or more. In this 
method the clear water is continuously discharging at a com- 
paratively low rate, the velocity in the reservoir being so small 
that the solid matter may be deposited as in the fill-and-draw 
method. Both of these methods are used, and both are effective. 
The choice will be dependent upon local conditions. In the 
continuous method the solid matter is largely deposited nearer 
the point of entrance into the reservoir, but more generally 
over the bottom in the fill-and-draw method. The velocity 
of flow in the reservoirs of the continuous method generally 
ranges between 0.5 inch and 2.5 inches per minute. Occasionally 
the velocity may be slightly less than the least of these values, 
and sometimes one or two inches more than the maximum value. 
216. Sizes and Construction of Settling- basins. — The sizes of 
the settling-basins will obviously depend to a considerable ex- 
tent upon the daily consumption of water. There is no general 
rule to be followed, but the capacity of storage volume of those 
actually in use run from less than i to possibly 14 or 15 days' 
supply. Under ordinary circumstances their volumes may 
usually be taken from 5 to 6 or 8 days' supply. Their shape 
should be such as to allow the greatest economy in the construc- 
tion of embankments and bottoms. They may generally be 
made rectangular. Their depths is also a matter, to some extent, 
of constructive economy. The depth of water will usually be 
found between about 10 and 16 feet, it being supposed that possibly 
2 or 3 feet of depth will be required for the collection of sedi- 
ment. These basins must be water-tight. The bottom surfaces 
may be covered with concrete 6 to 9 inches thick, with water- 
tight firm puddle 12 to 18 inches thick underneath, resting on 
firm compacted earth. The inner embankment surfaces or 
slopes may be paved with 10- or 12 -inch riprap resting on about 
18 inches of broken stone over a layer of puddle of equal thick- 



TWO METHODS OF FILTRATION. 281 

ness with the bottom and continuous with it. Occasionally the 
bottom and sides may be simply puddled with clay and lined 
with brick or riprap pavement, laid on gravel, or broken stone. 
It is only necessary that the sides and bottoms shall be tight 
and of such degree of hardness and continuity as to admit of 
thorough cleaning. 

The bottoms of sedimentation-basins may advantageously 
not be made level. In order to facilitate cleaning away the 
solid matter settling on them, a valley or depression may be 
formed along the centre line to which the two portions of the 
bottom slope. A grade in this channel or central valley of i in 500 
with slopes on either side of i in 200 or i in 300 will be effective 
in the disposition of the solid matter. At the lowest end of the 
central valley there should be suitable gates through which the 
accumulated sediment can be moved out of the basin. 'This 
sedimentary matter will in many cases be soft mud, but its 
movement will always be facilitated by the use of suitable streams 
of water. The frequency of cleaning will depend upon the 
amount of sediment carried by the water and upon its accumula- 
tion in the basin. Whenever its depth ranges from i to 2 or 3 
feet it is removed. 

Complete control of the entrance of the water to and its exit 
from the basin must evidently be secured by suitable gates or 
valves and other appliances required for the satisfactory oper- 
ation of the basin. In some cases the cost of sedimentation- 
reservoirs with concrete bottoms and sides has risen as high as 
$9000 per million gallons of capacity ; but where the cheaper 
lining has been used, as in the case of reservoirs at Philadelphia, 
the range has been from about $3300 to about $4300. 

217. Two Methods of Filtration. — After the process of sedi- 
mentation is completed there will necessarily always be found 
the remains of organic matter and certain other polluting material 
which should be removed before the water is allowed to enter 
the distributing system. This removal is accomplished usually 
by filtration through clean sand, but occasionally through porous 
material, such as concrete slabs, porcelain, or other similar 
material. The latter processes are not much used at the present 
time, and they will not be further considered. 



282 WATER-WORKS FOR CITIES AND TOWNS. 

The filtration of water through sand is carried on by two 
distinct methods, one called slow sand filtration and the other 
rapid sand filtration. In the first method the water is simply 
allowed to filter slowly through beds of sand from 2 to 3 or 5 feet 
thick and suitably arranged for the purpose. In the second 
method special appliances and conditions arc employed in such 
manner as to cause the water to flow through the sand at a much 
more rapid rate. The method of slow sand filtration will first 
receive attention. 

218. Conditions Necessary for Reduction of Organic Matter. — 
The most objectionable class of polluting materials includes 
organic matter which from one source or another finds its way 
into natural waters. Such material has originally constituted 
or formed a part of living organisms and chemically consists of 
varying proportions of carbon, oxygen, hydrogen, and nitrogen. 
As found in public water-supphes it is usually in some stage of 
decomposition. The chemical operations taking place in these 
decompositions are more or less complicated, but in a general 
way it may be said that the first step is the oxidizing of the car- 
bon which may produce either carbon monoxide or carbon dioxide 
and a combination of nitrogen with hydrogen as ammonia. When 
the conditions are favorable, i.e., when free oxygen is present, 
the ammonia may be oxidized by it, thus producing nitric acid 
and water. If, as is generally the case, suitable other substances, 
as alkalis, are present, the nitric acid combines with them, form- 
ing nitrates more or less soluble and essentially innocuous. It is 
therefore seen that the complete result is a chemical change from 
the original organic matter, offensive and possibly dangerously 
polluting, to gaseous and solid matter, the former escaping from 
the water and the latter either passing off un objectionably in a 
soluble state or precipitating to the bottom as inert mineral 
matter. In order that these processes may be completely effec- 
tive, two or three conditions are necessary, i.e., sunlight, free 
oxygen, and certain species of that minute and low class of organ- 
isms known as bacteria, the nature and conditions of existence 
of which have been scientifically known and studied within a 
period extending scarcely farther back than ten or fifteen years. 
The precise nature of their operations and their relations to the 



SLOW FILTRATION THROUGH SAND. 283 

presence of the necessary oxygen, or just the parts which they 
play in the process of decomposition, are not completely known, 
although much progress has been made in their determination^ 
It is positively known that their presence and that of uncom- 
bined oxygen are essential. Certain species of these bacteria 
will live and work only in the presence of sunlight and oxygen; 
these are known as aerobic bacteria. Other species, forming a 
class known as anaerobic bacteria, live and effect their opera- 
tions in the absence of sunlight and oxygen in that offensive 
mode of decomposition which takes place in cesspools and other 
closed receptacles for sewage and waste matter. They play an 
essential part in what promises to be one of the most valuable 
methods of sewage-disposal in which the septic tank is a main 
feature. 

219. Slow Filtration through Sand — Intermittent Filtration. — 
In the slow sand-filtration method of purifying the water of a 
water-supply the aerobic bacteria only act. In order that their 
operations may be completed, free oxygen and sunlight are 
essential requisites, and the first of these is found in every natural 
water which can be considered potable. Any water which does 
not contain sufficient free oxygen for this purpose is to be re- 
garded with suspicion, and generally cannot be considered suitable 
for domestic purposes. The amount of uncombined oxygen 
contained in any potable natural water is greatly variable and 
changes much with the period of exposure in a quiet state, as 
well as with pressure and temperature. In the river Seine it 
has averaged nearly 11 parts in a million throughout the year, 
being lowest in July and August and highest in December and 
January. It has been found in the experimental work of the 
Massachusetts State Board of Health that free or dissolved 
oxygen in potable water may vary from 8.1 parts at 80° Fahr. 
to 14.7 parts by weight at 32° Fahr. in 1,000,000 at atmospheric 
pressure. 

In some cases where liability to dangerous contamination 
exists it may be advisable to increase the available supply of 
oxygen in the water by using a slow sand filter intermittently, 
as has been done at Lawrence, Mass. Instead of permitting a 
continuous flow of water through the sand, that flow is allowed 



284 



WATER-WORKS FOR CITIES AND TOWNS. 



for a period of 6 to 12 hours only, after which the filter rests and 
is drained for perhaps an equal period. During this intermis- 




sion another filter-bed is brought into use in the same manner. 
Alternating thus between two or more filters, the flow in any 



SLOW FILTRATION THROUGH SAND. 



285 



one is intermittent. In this manner the oxygen of the air finds 
its way into the sand voids of each drained filter in turn and thus 
becomes available in the presence of suitable species of bacteria 




N0.1. CROSS-SECTION AT NORTH END OF BED. 




NO. 2. CROSS-SECTION AT BEGINNING OF PIPE UNDERDRAIN. 




N0.4. CROSS-SECTION AT END OF LOWEST GRAVEL UNDERDRAIN. 
SCALE IN FEET 




EUEV 29 
1,5. LONGITUDINAL SECTION OF A BED, AT WESTERLY END OF FILTER. 

SCALE IN FEET 

'--■■■ 



10 



20 



40 



SO 



TYPICAL SECTIONS OF UNIT BEDS IN LAWRENCE CITY FILTER. 

APRIL, 1901. 
COPIED FROM PLAN FURNISHED BY A. D. MARBLE, CITY ENGINEER. 

for reducing the organic matter in the water next passing through 
the filter. Intermittent filters operated in this manner are not 
much used, but the most prominent instance is that at Lawrence, 
Mass. At that place the water after being filtered is pumped 
to a higher elevation for use in the distribution system. The 



286 WATER-WORKS FOR CITIES AND TOWNS. 

pumps have been run nineteen hours out of the twenty-four, and 
the water is shut off from the filters five hours before the pumps 
stop. The gate admitting water to the filter is open one hour 
before they start. Nine hours of each day the filter does not 
receive water, and rests absolutely about four hours. 

220. Removal of Bacteria in the Filter. — The grains of the 
sand at and near the surface of a slow sand filter, within a short 
time after its operation is begun, acquire a gelatinous coating, 
densest at the surface and decreasing rapidly as the mass of 
sand is entered. This gelatinous coating of the grains is organic 
in character and probably largely made up of numerous colonies 
of bacteria whose presence is necessary for the reduction of the 
organic matter. It is necessary to distinguish between these 
species of bacteria and those which are pathogenic and charac- 
teristic of such diseases as typhoid fever, cholera, and others 
that are water-borne. Every potable surface-water and possibly 
all rain-water carry bacteria which are not pathogenic and which 
apparently accumulate in dense masses at and near the surface 
of the slow sand filter. As the water finds its way through the 
sand it loses its organic matter and its bacteria, both those of a 
pathogenic and non-pathogenic character. Potable water, there- 
fore, is purified and rendered innocuous by the removal in the 
filter of all its bacteria, including both the harmless and dan- 
gerous. 

221. Preliminary Treatment — Sizes of Sand Grains. — In de- 
signing filtration-works consideration must be given to the charac- 
ter of water involved. There are waters which when standing 
in open reservoirs exposed to the sunlight will develop disagree- 
able tastes and odors, and it may be necessary to give them pre- 
liminary treatment especially for the removal of such objection- 
able constituents. 

The character and coarseness of the sand employed are both 
elements affecting its efficiency as a filtering material. It should 
not be calcareous, for then masses of it may be cemented together 
and injure or partially destroy the working capacity. Again, 
if it is too coarse and approaches the size of gravel, water may 
run freely through it without experiencing any purification. 
Much labor has been expended, especially by the State Board 



PRELIMINARY TREATMENT— SIZES OF SAND GRAINS. 287 



of Health of Massachusetts, in investigating the characteristics 
of sdnd and the sizes of grains best adapted to filter purposes. 
In that work it has become necessary to classify sands according 
to degrees of fineness or coarseness. The diameter of a grain 
of sand in the system of classification employed means the cube 
root of the product of the greatest and least diameters of a grain 
multiplied by a third diameter at right angles to the greatest 
and least. The " effective" size of any given mass of sand means 
the greatest diameter of the finest lo per cent of the total mass. 
There is also a term called the "uniformity coefficient." The 
uniformity coefficient is the quotient arising from dividing the 
greatest diameter of the finest 60 per cent of the mass by the 
greatest diameter of the finest 10 per cent of the same mass. 
These are arbitrary terms which have been reached by experience 
as convenient for use in classifying sands. Evidently absolute 
uniformity in size will be indicated by a uniformity coefficient 
of I, and the greater the variety in size the greater will be the 
uniformity coefficient. Sands taken from dift'erent vicinities and 
sometimes even from the same bed will exhibit a great range in 
size of grain. 



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Fig. 5, — Sizes of Grain or Fineness of Sand. 

Fig. 5 represents the actual variety of size of grain as found in 
eight lots of sand among others examined in the laboratory of 
the Massachusetts State Board of Health. The vertical scale 



288 WATER-WORKS FOR CITIES AND TOWNS. 

shows the per cent by weight of portions having the maximum 
grains less in diameter than shown on the horizontal line. The 
more slope, like No. 5 or 6, the greater is the variety in size of 
grain. Those lines more nearly vertical belong to sands more 
nearly uniform in size of grain. 

222. Most Effective Sizes of Sand Grains. — Investigations by 
the Massachusetts State Board of Health indicate that a sand 
whose effective diameter of grain is .2 mm. (.008 inch) is perhaps 
the most efficient in removing organic matter and bacteria from 
natural potable waters. At the same time wide experience with 
the operation of actual filters seems to indicate that no particular 
advantage attaches to any special size of grain, so long as it is 
not too fine to permit the desired rate of filtration or so coarse as 
to allow the water to flow through it too freely. Experiments 
have shown that effective sizes of sand from .14 to .38 mm. in 
diameter possess practically the same efficiency in a slow sand 
filter. The action of the filter is apparently a partial straining 
out of both organic material and bacteria, but chiefly the reduc- 
tion of organic matter in the manner already described and 
probably the destruction to a large extent of the bacteria, espe- 
cially those of a pathogenic nature, although at the present time 
it is impossible to state the precise extent of either mode of action. 

223. Air and Water Capacities. — Another important physical 
feature of filter-sands, especially in connection with intermittent 
filtration, is the amount of voids between the grains. When 
the intermittent filter is allowed to drain, so that the only water 
remaining in it is that held between the grains by capillary attrac- 
tion, generally at the bottom of the filter unless the sand is very 
fine, the volume of the water which remains in the voids is called 
the water capacity of the sand. The remaining volume between 
the grains is called the air capacity of the same sand. It is evi- 
dent that the air capacity added to the water capacity will make 
the total voids between the sand grains. 

Fig. 6 shows the amount of air and water capacities of the 
same sands whose sizes of grains are exhibited in Fig. 5. The 
depth of the sand is supposed to be 60 inches, as shown on the 
vertical line at the left of the diagram, while the percentages of 
the total volume representing the amounts of voids is shown on 



AIR AND WATER CAPACITIES. 



289 



the horizontal line at the bottom of the diagram. Both air 
and water capacities for each sand are shown by the various 
numbered lines partially vertical and partially inclined. It 
will be observed that the fine sands No. 2 and No. 4 have 
large water capacities, the water capacity being shown by 



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per cent by volume 
Fig. 6. 

that part of the diagram lying below and to the left of each 
line. It will be noticed that No. 5 sand is made up of ap- 
proximately equal portions of fine and coarse grains, the former 
largely filling the voids between the latter. This mixture, 
as shown by the No. 5 line, gives a very high water capacity 
and a correspondingly low air capacity. Obviously a sand with 
a high water capacity has a correspondingly low air capacity, 
and in general would not be a very good sand for an intermittent 
filter, since it is the purpose of the latter to secure in the voids 



290 WATER-WORKS FOR CITIES AND TOWNS. 

between the sand grains as much oxygen as practicable whenever 
the filter may be at rest. 

224. Bacterial Efficiency and Purification — Hygienic Efficiency. 
— As the function of a filter is to remove as far as possible the 
organic matter and bacteria of the applied water, there must be 
some criterion by which its efQciency in the performance of those 
functions can be expressed. The bacterial efficiency is represented 
by the ratio found by dividing the number of bacteria after filtra- 
tion in a prescribed cubic unit, as a cubic centimeter, by the num- 
ber which the same volume of raw water held before being ap- 
plied to the filter. This is a rather misleading ratio, for the reason 
that the effluent water may contain bacteria of certain species 
which grow in the lower portions of a filter or in the drains which 
conduct the effluent from it. It is possible, therefore, that 
bacteria may be found in a filter effluent when all of the bacteria 
originally held in the water have been removed. Hence the 
ratio expressing what is called the bacterial purification arises 
from dividing the number of bacteria actually removed from a 
cubic centimeter of water by the filter by the number originally 
held by a cubic centimeter of raw water. The smaller the first of 
these ratios the higher the degree of efficiency. Extended expe- 
rience, both in the filters of such laboratories as that of the Mas- 
sachusetts State Board of Health and with actual filters of public 
water-supplies, show that under attainable conditions of opera- 
tion 98 to 100 per cent of all the bacteria originally found in the 
water may be removed. 

There is also used the term hygienic efiiciency which is used 
in connection with slow sand filters. This means simply the per 
cent of pathogenic bacteria removed by the filter, and there is 
good reason to believe that it is at least as high as the bacterial 
purification. 

225. Bacterial Activity near Top of Filter. — ^The work of re- 
moval of bacteria and organic matter has been found by extended 
investigations to be performed almost entirely wdthin 6 or 8 
inches of the top surface of the sand; indeed the most active 
part of that operation is probably concentrated Vithin less than 
3 inches of the surface. At any rate the retained bacteria and 
nitrogenous matter are found to decrease very rapidly within a 



RATE OF FILTRATION. 291 

ioot from the upper surface, below which stratum the quantity 
is relatively very small and its rate of decrease necessarily slow. 
A little of this nitrogenous or gelatinous matter is found to sur- 
round to a slight extent the sand grains found at the bottom of 
the filter. Some authorities have considered that the more 
steady uniform efficiency of the deeper filters is due to this effect. 

226. Rate of Filtration. — The rate at which water can be 
made to flow through a slow sand filter is of economical impor- 
tance, for the reason that the higher the rate the less will be the 
area required to purify a given quantity per day. Foreign 
engineers and other sanitary authorities advocate generally slower 
rates of filtration than American engineers are inclined to favor. 
The usual rate in Europe is not far from 1.6 to 2.5 million gallons 
per acre per day. There is also considerable range in this country, 
and the rate may reach 3 million gallons per acre per day. 
Indeed a considerable number of tests have shown that for 
short periods of time, at least, some waters may be efficiently 
filtered at rates as high as 7 to 8 million gallons per acre per day, 
but probably no American engineer is ready to introduce such 
high rates as yet. As a matter of fact the rate will depend con- 
siderably upon the character of water used. Clear water from 
mountain lakes and streams uncontaminated and carrying little 
solid material may be filtered safely and properly at much higher 
rates of filtration than river or other waters carrying more sedi- 
ment and more organic matter. This principle is recognized 
both in Europe and in this country. It would appear from 
experience that slow sand filters at the present time with rates 
of 2.5 to 3 million gallons per acre per day may be employed for 
practically any water that may be considered suitable for a public 
supply, and that with these rates high degrees of both bacterial 
purification and hygienic efficiency may be reached. 

227. Effective Head on Filter. — Inasmuch as the depth of 
sand ranges from perhaps 3 to 5 feet the water will experience 
considerable resistance in flowing through it. The distance in 
elevation between the water surface over the filter and that 
of the water as it leaA^es the filter measures the loss of head 
experienced in passing through the sand and the drainage- 
passages under it. It has been maintained by some foreign 



392 WATER-WORKS FOR CITIES AND TOWNS. 

authorities that this loss of head should be not more than 24 to 
30 inches ; that a greater head would force the water through the 
sand at such a rate as to render desired purification impossible. 
Experience both in the laboratory and with public filters in 
this country does not appear to sustain that view of the matter ; 
considerably greater heads than 30 inches have been used with 
entirely satisfactory results both as to the removal of organic 
matter and bacteria. It appears to be best so to arrange the flow 
of water through the sand and the underdrains as to avoid in 
either a pressure below the atmosphere, as in that case some of 
the dissolved air in the water escapes and produces undesirable 
disturbances in the sand, resulting in reduced efficiency. No 
precise rule can be given in respect to this feature of filtration, 
but it seems probable that satisfactory results may be obtained 
under proper working of filters with a loss of head not greater 
than the depth of water on the filter added to the depth of sand 
in it, although that maximum limit would ordinarily not be 
reached. The depth of water on the filter may be taken from 
3 to 5 feet. In this country it is seldom less than the least of 
these limits, and perhaps not often equal to the greater limit. 

228. Constant Rate of Filtration Necessary. — Care should be 
taken in the operation of filters to avoid any sudden change in 
the texture or degree of compactness of the sand. At the times 
when workmen must necessarily walk over the surface they 
should be provided with special broad-based footwear, so as to 
produce as little effect of this kind as possible where they step. 
Sudden changes in the degree of compactness cause correspond- 
ingly sudden changes in the rate of filtration, and such changes 
produce a deterioration of efficiency. This may be due to two 
or three reasons. Possibly such changes may open small chan- 
nels through which water finds its way too freely ; or the break- 
ing of the gelatinous bond between the grains of sand may operate 
prejudicially. At any rate it is essential to avoid such sudden 
changes and maintain as nearly uniform a rate of filtration over 
the entire filter as possible. Again, the age of a filter affects to 
some extent its efficiency. A month or two of time is required, 
when a new filter is started, to attain what may be called its 
normal efficiency. Even after that length of time the filter gains 



SCRAPING OF FILTERS. 293 

in its power to retain and destroy bacteria. This action is par- 
ticularly characteristic of filters formed of comparatively coarse 
sand. 

229. Scraping of Filters. — More or less solid inert as well as 
organic matter accumulates on the surfaces of the slow sand 
filters, so that at t_ .id of proper periods of time, depending upon 
the character of the water filtered, this surface accumulation must 
be scraped off and removed together with the sand into which 
it has penetrated. In scraping the filter it is impossible to re- 
move less than .25 or .5 inch of sand, and at least .5 to .75 inch 
is removed whenever a filter is scraped. Sometimes i or 2 inches 
may be removed. This sand may be washed and again placed 
upon the filter for use. The operation of scraping exhibits a 
fresh sand surface to the applied water. It has been held, par- 
ticularly by foreign authorities, that this operation of scraping 
militates against the efficiency of the filter for the time being. 
The investigations of the Massachusetts State Board of Health 
and other experiences in this country do not confirm that view 
which is based on the assumption that the top nitrogenous film 
is essential to efficienc}^ These investigations have shown that 
this film is not necessary in intermittent filters; that in many 
instances no diminution of efficiency has resulted from a removal 
of the film to a depth of .3 inch; that even the presence of that 
film has not given efficiency to coarse sand when the coating was 
thick enough to completely clog the filter; and, further, that 
the material of this nitrogenous film is found at a depth of sev- 
eral inches below the surface. It is practically certain that the 
scraping to depths not exceeding i inch have no sensible effect 
upon the efficiency under proper management and operation of 
the filters. This is particularly true if the thickness of sand is 
from 3 to 5 feet. It is undoubtedly true that with ver\^ shallow 
sand filters from i to 2 feet in depth the scraping of the surface 
may have some effect upon bacterial efficiency. 

It has been the custom in connection with some European 
filters to waste the water which first passes through after clean- 
ing, but the usual practice in this country is to fill slowly the filter 
with filtered water from below and, after the sand is submerged, 
to hermit it to stand a little while before use. Care taken in 



294 WATER-WORKS FOR CITIES AND TOWNS. 

this manner will insure an efficiency to a freshly scraped filter 
sufficient to avoid any wastage. 

230. Introduction of Water to Intermittent Filters. — Where 
intermittent filters are used it is of the greatest importance to 
conduct the water to them so as not to disturb the sand on their 
surfaces. This can readily be done in a number of ways. If the 
shape of the filter is not oblong, it will be advisable to form a num- 
ber of main drains or passages in the sand from which smaller 
depressions or passages near together may lead the water to all 
parts of the surface. The flowing of the first water through these 
depressions will permit the entire surface to be covered so grad- 
ually as not to disturb the sand grains, and it is essential that 
such means or their equivalent be employed. If the filter is 
long and narrow in shape, the main ditch along one of the longer 
sides, with depressions at right angles to it or across the filter 
and near together, will be sufficient to accomplish the desired 
purpose. Obviously when filters are not intermittently used 
such precautions are not needed. 

231. Effect of Low Temperature. — In the early days of the 
use of sand filters in this country it was frequently supposed that 
the low temperature of the winter caused decreased bacterial 
purification and a decrease in power to reduce organic material. 
It now appears that such is not the case. The effects of low 
temperature, such as is experienced in winters of this climate, 
may be overcome by temporarily covering the filters so that 
heavy ice cannot form and produce disturbances in one way or 
another prejudicial to efficiency of operation. The agencies 
which operate to reduce efficiency in cold weather are no longer 
believed to be those due to low temperature. They are rather 
indirect and mechanical, and may be readily overcome by the 
prevention of the formation of ice. 

232. Choice of Intermittent or Continuous Filtration. — The 
process of slow sand filtration when continuous has been shown 
by experience to be entirely effective for ordinary potable waters, 
but in those cases where the amount of dissolved oxygen may be 
low and where the amount of organic matter is relatively high 
it may be advisable to resort to intermittent filtration. Neither 
method, however, can be depended upon to render potable a 



SIZE AND ARRANGEMENT OF SLOW SAND FILTERS. 395 

water which has been robbed of its free oxygen by an excessive 
amount of contaminated organic matter. Nor can these processes 
be expected to remove coloring matter produced by peaty soils 
or other conditions in which large amounts of vegetable matter 
have been absorbed by the water. The methods, therefore, 
have their limitations, although their field of application is 
sufficiently wide to cover nearly all classes of potable water. 

233. Size and Arrangement of Slow Sand Filters. — Among 
the first questions to arise in the design of slow sand filters are 
their size and arrangement. The total area will be determined 
by the total daily draft and the rate of filtration. Rates of filtra- 
tion running from 2.5 to 3 million gallons per acre per day, or 
even more, have been found satisfactory and are customary in 
this country. Having given, therefore, the total daily quantity 
required, it is only necessary to divide that by the rate of filtration 
per acre and the result will be the number of acres required for 
the total filter-bed surface. This net area, however, is not suffi- 
cient. Unless there is requisite storage of filtered water to meet 
the variation in the hourly draft for the day, the capacity of the 
filters must be sufficient to meet the greatest hourly rate, which 
must be taken at least i^ times the average hourly demand 
during the day ; indeed this is only prudent in any case. 

Again, it is necessary to divide the total filter surface into 
small portions called beds, so that one or more of them may be 
withdrawn from use for cleaning or repairs, while a sufficient 
filter-area remains in operation to supply the greatest hourly 
draft. This surplus area will usually run from 5 to 20 per cent 
of the total area of the filter-beds, although for small towns and 
cities it may be much more. The sizes of the filter-beds will 
depend upon the local circumstances of each case. It is evident 
that as each single bed must have its individual set of appliances 
and its separating walls, the purpose of economy will be best 
served by making the beds as large as practicable. At the same 
time they must not be made too large, for in that case the portion 
out of use might form so large a percentage of the total area as 
to increase unduly the cost of the entire plant. A size of bed 
varying between .5 and 1.5 acres is frequently and perhaps gen- 
erally found in foreign filtering-plants. If filter-beds range in 



296 WATER-WORKS FOR CITIES AND TOWNS. 

area from .5 acre to 2 acres, the latter for large plants, the pur- 
poses of economy and convenience in administration will probably 
be well served. The grouping of the beds is an important con- 
sideration and will depend somewhat, at least, upon the shape 
of the plot of ground taken for the filters. It is advisable that 
the inlets to the different beds should, as far as possible, discharge 
from a single inlet-pipe or main. This will generally be most 
conveniently accomplished by making the beds rectangular in 
shape, grouped on each side of the supply -main, with their longest 
dimensions at right angles to it. This arrangement is illustrated 
by the grouping of the filter-beds in the Albany plant, shown in 
Fig. 7. In the case of a single oblong bed, like that at Lawrence, 
Mass., shown in Fig. 4, page 284, its relatively great length and 
small width makes it possible to run the main supply along one 
side, from which branch depressions with concrete bottoms enable 
the water to be distributed uniformly over its surface in the man- 
ner shown in the figure. It is further necessary to group the 
filter-beds, pumps, sand-cleaning appliances, and other portions 
of the plant, so that the ends of economy and efficient adminis- 
tration may be served in the highest degree. It is always neces- 
sary that these features of the whole filtration system should be 
carefully kept in view in laying out the entire plant. 

234. Design of Filter-beds. — The preparation of the site for a 
group of filtration-beds also involves the consideration of a num- 
ber of principal questions. In the first place, the depth required 
for the sand and underdrains will not be far from 5 feet, and there 
must be a suitable bottom prepared below the collecting-drains. 
Again, the depth of water above the sand may vary from 3 to 5 
feet, making the total depth, including the bottom, of the filter 
proper about 10 or 11 feet, and this may represent the depth of 
excavation to be made. If the material on which the filter to be 
built is soft, it may be necessary to drive piles to support the 
superincumbent weight. The bottom must be made water- 
tight. This can be done either by the use of a layer of well 
rammed or packed clay, i to 2 feet in thickness, carrying 6 or 8 
inches of concrete, or by a surface of paved brick or stone. If 
the sides of the filter-beds are of embankments with surface 
slopes, the latter may be protected in the same manner. If the 



DESIGN OF FILTER-BEDS. 



297 



sides are of walls of masonry, concrete is an excellent material to 
be used for the purpose. 





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through the sand for the support of the roof, in case there is one, 



298 



WATER-WORKS FOR CITIES AND TOWNS. 



it is imperative that care be taken to prevent water from flowing 
down through the joints between the sand and the sides of piers 




or the masonry sides of the filter-beds. There should be no 
vertical joint of that character, but the faces of masonr}^ in con- 



COVERED FILTERS. 299 

tact with the sand should both slope and be made in steps, so 
that any settlement of the sand will tend to close the joint, while 
the steps will prevent flow. Nor should there be angles in which 
sand is to be packed ; filleted corners are far preferable and should 
be used. 

235. Covered Filters. — It has become the custom where the 
best results are expected in cold climates, if not in all cases, to 
cover filters with masonry roofs of domes and cylindrical or groined 
arches supported on masonry columns. Such roofs are usually 
covered with earth to a depth of i to 2 or 3 feet. They prevent 
any injurious action on the sides of the filters produced by thick 
ice or the effects of such ice upon the upper portions of the sand. 
In summer they also protect against the baking and cracking of 
the upper surface of the sand when exposed to the sun and pre- 
vent, to a considerable extent,' the growth of algee in different 
portions of the beds. They are expensive, filters with masonry 
covers costing once and a half to twice as much as open filters, but 
they enhance the sanitary value of the water. The height of 
the masonry roof must be about 2 to 3 feet above the upper 
surface of the water and high enough to offer convenient access 
to the sand when it is to be cleaned and renewed. The length 
of span for the arches or domes is seldom more than 12 or 15 feet. 

236. Clear-water Drain-pipes of Filters. — After the water has 
passed through the sand it must be withdrawn from the bottom of 
the filter with as little resistance as practicable. This necessi- 
tates, in the first place, the bottom of the filter to be so shaped 
as to induce the flow of the filtered water toward the lines of 
drain-pipes which are laid to receive it. These pipes consist of 
the main members and the branches, the main members being 
laid along the centres of the beds and the branches running from 
them. The bottoms of the filters, therefore, should be formed 
with depressions in which the main pipes are laid, and with such 
grades as to expedite the movement of the water flowing through 
the branches. If the bottoms are of concrete, they can advan- 
tageously be made of inverted arches or domes, the drain-pipes 
being laid along the lines of greatest depression. In such cases the 
loads produced by the weight of the roof are more nearly uni- 
formly distributed over the bottom. The sizes of the drains will 



300 WATER-WORKS FOR CITIES AND TOWNS. 

be dependent upon the areas from which they withdraw water. 
It is advisable to make them rather large-, in order that the water 
may flow through them more freely. They seldom need exceed 
6 or 8 inches. They are preferably made of salt-glazed vitrified 
pipes laid with open joints, around and in the vicinity of which 
are placed gravel or broken stone, the largest pieces with a 
maximum diameter of i to 2 inches. The largest broken stone 
or coarsest gravel is near the pipe and should decrease in size as 



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Interior of Covered Filter at Ashland, Wis. 

the drain-pipe is receded from, so that the final portions of the 
gravel farthest removed from the drains will not permit the filter- 
sand to pass into it. When properly designed and arranged, the 
loss of head in passing from the farthest points of a filter-bed to 
the point of exit from the filter will not exceed about .oi to .02 of 
a foot. 

237. Arrangement of the Sand at Lawrence and Albany. — ^Above 
this gravel is placed the filtering-sand, about 4 feet thick in the 
Albany filter and 3 to 4 feet thick in the filter at Lawrence, Mass. 
The sand in the Albany filter was specified to have not ' ' more than 
10 per cent less than .27 mm." in diameter and "at least 10 per 



ARRANGEMENT OF SAND AT LAWRENCE AND ALBANY. 301 

cent by weight shall be less than .36 mm." in diameter. Over 
the entire floor was spread not more than 1 2 inches of gravel or 
broken stone, the lower 7 inches consisting of broken stone or 
gravel with greatest diameter varying from i inch to 2 inches ; 
the remaining 5 inches of the lower i foot was composed of 
broken stone or gravel decreasing from i inch in greatest diam- 
eter to a grain a little coarser than that of the sand above it. In 
all cases, sand for the filter-bed should be free from everything 
that can be classed as dirt, including clay, loam, and vegetable 
matter. Furthermore, it should be free from any mineral matter 
which might change the character of the water and render it less 
fit for use. 

This filtering-sand is usually placed in position with a hori- 
zontal surface. At Lawrence, however, it was placed with 




Partially Filled Covered Sand Filter showing Drain pipe. 

a wavy surface, the horizontal distance between the crests 
of two consecutive waves being 30 feet, the concrete gutter for 
admitting the water being half-way between, all as shown in 
the illustrations. The sand of this filter was of two grades, the 
coarser sand having an effective size of 0.3 mm. (.118 inch) and 
the finer an effective size of 0.25 mm. (.098 inch). The two dif- 



302 WATER-WORKS FOR CITIES AND TOWNS. 

ferent sizes of sand are seen not to be arranged in horizontal 
layers, but so that the finer is over the drains and the coarser 
between. The No. 70 sand is capable of passing 70 million gal- 
lons per acre per day with a head on it equal to the depth of 
sand, while the No. 50 sand can pass 50 million gallons per acre 
per day with a head on it equal to its depth. There appears to 
be no special advantage in placing the sand in filters other than 
in horizontal layers with an effective size practically uniform. 

238. Velocity of Flow through Sand. — The velocity with which 
water will fiow through a given depth of sand with a known 
depth or head above the surface of the latter has been carefully 
investigated by the Massachusetts State Board of Health with 
the following results : 

V = the velocity at which a solid column of water, whose sec- 
tion equals in area that of the bed of sand, moves down- 
ward through the sand in meters per day ; this is practi- 
cally the number of million gallons passing through the 
sand per acre per day. 

c = a constant, having the value of 1000 for clean sand, and 
800 for filter-sand after having been some time in use. 

d=the eft'ective size of the sand-grain in millimeters. 

h=th.e head lost by the water in passing through the sand at 
the rate v ; this is the effective head of water producing 
motion through the sand. 

/ = the thickness of the sand bed. 

^ =the temperature of the water in degrees Fahr. • 

The velocity v, as determined by experiment, takes the fol- 
lowing form: 

V = ca- 



lx 60 

This formula cannot be used for the flow of water through all 
sands of all thicknesses and under all circumstances. It is lim- 
ited to effective diameters of sand between .1 and 3 mm., having 
a uniformity coefficient not greater than 5. h and / may be 
taken in any unit as long as both are expressed in the same unit, 
since the ratio of the two quantities will then not be affected. 



FREQUENCY OF SCRAPING. 303 

If the effective head of water on the filter or the liead lost is equal 
to the thickness of the bed of sand, the ratio of h divided by / 
will be I . In case the formula is used to express the quantity of 
water flowing through the sand per acre per day, it must be 
remembered that v will be the number of million gallons and 
not the total number of gallons. The formula can only be used 
when the sand is well compacted and where the voids of the 
sand are entirely filled with water. 

239. Frequency of Scraping and Amount Filtered between Scrap- 
ings. — The frequency of the scraping of filters will depend upon 
the amount of organic matter in the water and upon the rate of 
filtration. Between the years 1893 and 1900 the periods between 
scrapings of the Lawrence filter ranged generally from 20 to 32 
days, although periods as small as 13 or 19 are found in the 
records. The quantity of water passed between scrapings varies 
generally from 67 million to 90 million gallons, although it fell 
as low as 49 millions and rose as high as 109 millions. In the 
case of the Albany filter-plant, up to the end of the year 1900 
the shortest period between scrapings was about 15 days and 
the longest about 42 days, the smallest quantity of water passing 
through any filter between scrapings being 26,735,000 gallons 
and the largest 76,982,000 gallons. The operation of the Albany 
filters for the year 1901 shows that the average run of a bed was 
26 days between scrapings, with a total of 70,000,000 gallons per 
acre for that period. These figures represent about the usual 
workings of slow sand filters at the present time, the period 
between scrapings running usually between 15 and 30 days, and 
the quantity from 30 million gallons per acre to 100 million 
gallons per acre. 

240. Cleaning the Clogged Sand. — The clogged sand scraped 
from the top of the filters at the periods of cleaning is removed 
to a convenient point where appliances and machinery are avail- 
able for washing it. This is an item of some importance in the 
administration of filters, as the sand which is removed and 
washed is at a later period replaced upon the filter-bed. Various 
methods have been tried for the purpose, of cleaning sand effi- 
ciently and economically. The continuous ejector sand- washer, 
one set of which is used at Albany, is probably as efficient as any 



304 



WATER-WORKS FOR CITIES AND TOWNS. 





CONTROLLING OR REGULATING APPARATUS. 305 

machine yet devised. It is shown in Fig. 8. It will be observed 
that the dirty sand is fed to the machine at one end into a hopper- 
shaped receptacle. In the bottom of this hopper is a nozzle 
through which water is discharged from a pipe running along 
the entire bottom of the machine. This jet of water forces the 
sand upward through a suitable pipe into a reservoir which dis- 
charges the sand and water into another hopper, and so on through 
the series of five. Evidently there may be any number of hop- 
pers in the series, a jet of water being provided at the bottom of 
each. In this manner the sand and water are thoroughly mixed 
together and compelled to flow upward from each hopper to the 
next, the dirty water overflowing also from each hopper into a 
tank underneath, whence it runs to waste. The clean sand and 
water flow out of the machine at the end opposite to that at 
which they entered. After the washed sand is dried it is ready 
to be replaced in the filter. 

241. Controlling or Regulating Apparatus. — It is essential to 
the proper working of a slow sand filter that the amount of water 
admitted to and passing through it shall be as nearly uniform as 
practicable. This necessitates controlling or regulating appara- 
tus, of which there are two general classes, the one automatic 
and the other worked by hand. There are a considerable num- 
ber of appliances of both classes. The filtered water flows from 
the end of the drains to one or two small tanks formed by suit- 
able masonry walls immediately outside of the filter-beds and 
rises to a level determined by the loss of head in passing through 
the filter. The difference in elevation between the water surface 
over the sand and that in the filtered water-tanks shows the 
effective head which causes the water to flow through the sand. 
The object of the controlling or regulating appliances is to keep 
that head as nearly constant as possible. Both the hand and 
automatic appliances preserve the value of that head by main- 
taining constant discharges through either vertical or horizontal 
orifices, the orifices themselves being movable. They may be 
rectangular or other orifices with horizontal lips or crests. If the 
control is automatic it is accomplished usually by a float which 
raises and lowers the orifice in such a way as to maintain a con- 
stant difference of level between the filtered and the unfiltered 



306 



WATER-WORKS FOR CITIES AND TOWNS. 




COST OF SLOW SAND FILTERS. 



307 



water. The figures illustrate both types of regulating appliances, 
the actions of which will be readily understood. 

242. Cost of Slow Sand Filters. — The cost of both the open and 
covered slow sand filters will obviously vary according to the 
cost of labor and materials at their sites. The original cost of 
the Lawrence filter, about 2.44 acres in total area, was nearly 
$2 5 ,000 per acre. The cost of covered filters, so far as constructed 
in this country, varies from about $44,000 to nearly $51,000 per 




Reservoir WAvti. 




Tto REStRVOlft 



Fig. q. — Ball-float Regulator of Rate Fig. ic — Regulating Apparatus Designed 
of Filtration. by J. H. Fuertes for the Tome Institute 

Filters. 



acre excluding the pipe, pumping plants, and sedimentation- 
basins. The Albany covered filters cost about $38,000 per acre 
including filtering materials, but excluding excavation, pumps, 
buildings, sedimentation-basins, piping, and sand-washing ma- 
chinery, or nearly $46,000 per acre including those items except 
pumps and sedimentation-basins. The roof, included in the 
preceding estimate, cost about $14,000 per acre. The smaller 
the filters the greater the cost per acre, as a rule, as would be 
expected. A single open filter at Poughkeepsie and three open 
filter-beds at Berwyn, Pa., cost respectively $42,000 and $36,000 
per acre, the former being little less than .7 acre in area and the 



308 



WATER-WORKS FOR CITIES AND TOWNS. 



latter having an aggregate area of a little more than one-half acre. 
A covered filter at Ashland, Wis., consisting of three beds of one- 
sixth acre each, cost at the rate of about $70,000 per acre. 

243. Cost of Operation of Albany Filter. — The cost of operat- 
ing the Albany filter, including only the costs of scraping, remov- 




Fig. II. — Regulator of Rate of Filtration. 



^ 




Fig. 12. — Regulator of Rate of Filtration. 

ing sand, refilling, incidentals, lost time, and washing the sand 
during seventeen months ending December 29, 1900, was $1.66 
per million gallons filtered. The cost of removing the sand (ex- 



OPERATION AND COST OF OPERATION OF LAWRENCE FILTER. 309 

eluding scraping), washing, and refilling was $1.21 per cubic 
yard. The total cost of operating the entire filter-plant, includ- 
ing all items, for the year 1900 was $4.52 per million gallons 
filtered. This covers all expenses, including pumping, superin- 
tendence, and laboratory, which can be charged to the operation 
of the filter-plant. The average removal of albuminoid ammonia 
at Albany for the year 1900 was 49 per cent and of the free am- 




FiG. 13. — Regulator Designed by W. H. Lindley for the Filters at Warsaw, Poland. 



monia 78 per cent of that in the raw water, while the average 
bacterial removal was over 99 per cent, running from 98.3 per 
cent to 99.6 per cent. The volume of water used in washing 
the sand was about twelve and a half times the volume of the 
sand. Each cubic yard of sand washed, therefore, required twelve 
and a half cubic yards of water. 

244. Operation and Cost of Operation of Lawrence Filter. — It 
was originally intended that the Lawrence filter should be worked 
intermittently. The Merrimac River water, which is used by the 
city of Lawrence, was known to carry at certain periods of the 
year sufficient typhoid germs received from the city of Lowell 
to produce at least mild epidemics. The intermittent operation 
was considered necessary to furnish the filter with the requisite 
oxygen to destroy beyond a doubt all pathogenic bacteria. The 
increasing demands of water consumption during the years that 
have elapsed since filtration began in 1894 have seriously modi- 
fied these conditions, so that the intermittent feature of operation 
of the filter is no longer very prominent. During 1898, for 
instance, the filter was drained only four to thirteen times per 



310 WATER-WORKS FOR CITIES AND TOWNS. 

month, with an average of eight monthly drainings. In 1899 
the drainings were more frequent, varying from five to fourteen 
per month and averaging eleven times. Finally, in 1900, the 
monthly drainings ranged from three to thirteen, with an average 
of eight. It may be considered, therefore, that the Lawrence 
filter occupies a kind of intermediate position between inter- 
mittent and continuous operation. 

The total cost of operating the filter at Lawrence, including 
scraping and washing of sand, refilling, removal of snow and ice, 
and general items in the period from 1895 to 1900, both inclusive, 
varied from a minimum of $7.70 per million gallons to $9.00 per 
million gallons. If the removal of snow and ice be omitted, these 
amounts will be reduced to $5.10 and $6.90 respectively. The 
cost of washing the sand only in the Lawrence filter during the 
same period varied from 45 to 67 cents per cubic yard. The 
volume of water required for that washing varied from ten to 
fourteen times the volume of sand. 

245. Sanitary Results of Operation of Lawrence and Albany 
Filters. — The average number of bacteria in the Merrimac River 
water applied to the filter during the period 1894 to 1899, both 
inclusive, varied from about 1900 per cubic centimeter to 34,900, 
and the percentage of reduction attained by passing the water 
through the filter varied in the same period generally from 97 to 
99.8 per cent, with an average of about 99.1 per cent. 

In the city of Lawrence the average number of cases of typhoid 
fever per 10,000 of population has been about one third, since 
the introduction of filtered water, of the number of cases which 
existed prior to the installation of the filters, and less than one 
fourth as many deaths. A large number of the cases of typhoid 
occurring after the installation of the filter have been traced to 
the use of unfiltered water, and it is probable that all or nearly 
all could be similarly accounted for. 

In the city of Albany the experience had been quite similar. 
The average number of deaths per year from typhoid fever for 
ten years before the introduction of filtered water was 84, while 
in 1900, with the filter in operation, the total number of deaths 
was 39. These figures are sufficient to show the marked bene- 
ficial effect of filtered water on the public health. 



RAPID FILTRATION WITH COAGULANTS. 



311 



246. Rapid Filtration with Coagulants. — It has been seen that 
the rate of filtration through open sand filters does not usually 
exceed 2 to 4 million gallons per acre per day under ordinary 
circumstances. Much greater rates would clog the sand and 
produce less efficient results. Experience has also shown that 
such methods cannot be depended upon to remove from water 
coloring matter of a vegetable origin or very finely divided sedi- 
ment. In order to accomplish these ends it is necessary to 




Jewell Filter. 

employ suitable chemicals which, acting as coagulants, may 
accomplish results impracticable in the open filter. Resort has 
therefore been made first to the adoption of suitable coagulants 
and then to such increased heads or pressures as to force the 
water through the sand at rates from 25 to 30 or even 50 times 
as great as practicable in slow sand filtration. These rapid sand 
filters are called mechanical filters. If the water is forced through 



312 WATER-WORKS FOR CITIES AND TOWNS. 

them under pressure, they consist of closed tanks in which sand 
is placed so as to leave sufficient volume above it for the influent 
water and, supported upon a platform carrying perforated pipes, 
strainers, or equivalent details through which the filtered water 
may flow into a suitable system of effluent pipes in the lower part 
of the filter. If water is forced through the sand by the required 
head, the upper part of the filter may be open, but of sufficient 
height to accommodate it. The same filtering material, clean 
sand, is used as in the slow filters ; the only differences, aside from 
the higher rate of filtration, are the greater head and the intro- 
duction of a coagulant to the water. The depth of sand used 
may vary from 2 to 4 feet. The thickness of a relatively fine 
sand may be less than that of a coarser sand. 

247. Operation of Coagulants. — The coagulant which has been 
found to give the best results is ordinary alum or sulphate of 
aluminum. If sulphate of aluminum is dissolved in water con- 
taining a little lime or magnesia, aluminum hydrate and sulphuric 
acid are formed. The aluminum hydrate is a sticky gelatinous 
substance which gathers together in a flocculent mass the particles 
of suspended matter in the water, and it also adheres to the grains 
of sand when those masses have settled to the bottom. This 
flocculent, gelatinous mass covers the sand and passes into its 
voids. As the water is forced through it the bacteria and sus- 
pended matter are held, leaving a clear effluent to pass through. 
Other cdkgulants are used, such as the hydrate of iron, but it costs 
more than alum and is not so effective in removing color, although 
it is an excellent coagulant for removing turbidity. Physicians 
have made objection to the use of alum for this purpose, on the 
ground that any excess might pass into distribution-pipes and 
so be consumed by the water-users to the detriment of health. 
While it is possible that further experience may show that there 
is material ground for this objection, it has thus far not been 
found to be so. It is, however, essential that only the necessary 
amount of alum should be used and that there may be a sufficient 
amount of alkali to combine with the sulphuric acid. Otherwise 
the acidulated water may attack the iron and lead pipes and so 
injure the water and produce serious trouble. It can only be 
stated that the method and operation of these mechanical filters 



PRINCIPAL PARTS OF MECHANICAL FILTER-PLANT. 313 



have thus far been sufficiently successful to avoid any of these 
difficulties. 

248. Principal Parts of Mechanical Filter-plant — Coagulation 
and Subsidence. — The principal parts of a complete mechanical 
filter-plant in the order of their succession are a solution-tank, 
a measuring-tank, a sedimentation-basin, and a filter. In case 
of great turbidity the sedimentation may be completed in two 




The Jewell Filter-plant at Nunistuwu, Penn. 

stages, the first in a settling-basin prior to receiving the coagulant, 
and the second in another basin subsequent to the coagulation. 
The tanks are usually of wood, although they may be of steel. 
The solution-tank is a comparatively small vessel in which the 
alum is dissolved. The solution is then run into the measuring- 
tank, from which it flows into the water at a constant rate main- 
tained by suitable regulating apparatus. It is imperative for 
the successful working of the mechanical filter- plant that the 
coagulant be introduced to the water at a uniform rate. This 



314 WATER-WORKS FOR CITIES AND TOWNS. 

rate will obviously depend upon the character of the water. The 
coagulating solution runs from the measuring-tank into the pipe 
through which the water to be filtered flows and in which it first 
receives the alum. The water and the coagulating solution are 
thus thoroughly mixed and flow into the sedimentation-basin. 
The subsidence which is provided for in this basin may be omitted 
in very clear waters which carry little solid matter, but the 
operation of the filter itself will be more satisfactorily accom- 
plished if as much work as feasible is done before reaching it. 
The mixture must remain in this basin a sufficient length of time 
to allow such subsidence as can reasonably be attained. 

It appears from experience in this part of the work that it is 
not well to introduce the coagulant too long before the water 
enters the filter, especially if the water be fairly clear. In the 
case of the presence of finely divided solid matter, however, 
sufficient time must be permitted for the necessary settlement. 
A period ranging in length from ^ hour to 6 or 8 hours may be 
advantageously assigned to this part of the operation, the shorter 
period for clear waters and the longer for very turbid waters. 
It has been suggested that two applications of the coagulant 
might be beneficial, the principal portion being given to the water 
before entering the sedimentation-basin and the other just before 
the waters enters the filter. The work of the filter, especially 
with turbid waters, may be much reduced by simple subsidence 
for a period of perhaps 24 hours before receiving the coagulant, 
the secondary subsidence taking place in the settling-basin in 
the manner already described. Duplicate solution- and measur- 
ing-tanks will be required in order that the process may be con- 
tinuous while one set is out of use. In this process it is absolutely 
essential also that the coagulant should be of the best quality, 
inferior grades having been found to be unsatisfactory in their 
operation. 

249. Amount of Coagulant — Advantageous Effect of Alum on 
Organic Matter. — The amount of sulphate of alumina will vary 
largely with the quality of water. In the investigation made by 
Mr. Fuller in connection with the Ohio River supply for the city 
of Cincinnati, he found that with very slight turbidity only 
f grain was required per gallon of water, but that a high degree of 



HIGH HEADS AND RATES FOR RAPID FILTRATION. 315 

turbidity required as much as 4.4 grains per gallon, with inter- 
mediate amounts for intermediate degrees of turbidity. It was 
estimated that these quantities would correspond to an average 
annual amount of about 1.6 grains per gallon. In case there 
should be a period of three days of subsidence preliminary to 
filtration, he estimated that for the. greater part of the time the 
amount of alum would vary from i to 3 grains per gallon. Occa- 
sionally more and sometimes less would be required. 

Alum has some specially valuable qualities in connection with 
this class of purification work. It combines with coloring matter, 
particularly that which has been acquired from contact of the 
water with vegetation, and precipitates it. It seems to combine 
also, to some extent, with the organic matter carried by the 
water and thus enhances the efficiency of filtration. 

250. High Heads and Rates for Rapid Filtration. — The prin- 
cipal work of investigation of filtration in mechanical or pressure 
filters has been made for the cities of Pittsburg, Cincinnati, Louis- 
ville, and Providence, R. I. In the experimental work of those 
investigations rates of filtration ranging from 46 million to 170 
million gallons per acre per day have been employed with essen- 
tially the same efficiency. This is a practical result of great 
importance, particularly if in the continued use of these filters 
on a large scale a satisfactorily high efficiency can be reached and 
maintained. It was observed that the number of bacteria in the 
effluent varied with that in the raw water. It was also noticed 
that similarly to the operation of slow sand filters the rate of fil- 
tration should not be changed suddenly, as that is likely to cause 
breaks in the sand and militate against continued efficiency. 

In his experimental work at Cincinnati Mr. Fuller found that 
with fine sand an available head on the filter of 12 feet gave 
economical results. He also states that ' ' high rates are more 
economical than low ones, and that the full head which can be 
economically used should be provided. Just where the economi- 
cal limit of the rate of filtration is can only be determined from 
practical experience with a wider range of conditions than exist 
here, but there seem to be no indications that the capacity of a 
plant originally constructed on a medium rate basis (100 million 
to 125 million gallons per acre daily) could not readily and eco- 



316 WATER-WORKS FOR CITIES AND TOWNS. 

nomically be increased, as the consumption demanded, to rates 
at least as high as the highest tried here (170 milhon gallons per 
acre daily), provided the full economical increase in loss of head 
could be obtained." 

251. Types and General Arrangement of Mechanical Filters. — 
These mechanical or pressure (by gravity) filters have until lately 
been constructed by companies owning patents either on the 
process or on the different parts of the filters. The fundamental 
patent, however, protecting rapid sand filters with the continu- 
ous application of a coagulant has expired and the city of Louis- 
ville, Ky., is now constructing rapid sand filters different in 
design from those heretofore used. The types that have been 
most common heretofore are the Jewell subsidence gravity filter, 
the Continental gravity filter, the New York sectional-wash 
gravity filter, and others. They all possess the main feature of 
accelerating the rate of filtration by pressure, either in a closed 
tank (rarely) with comparatively small water volume above the 
sand or by an open filter with sufficient head of water above the 
sand to accomplish the high rate desired. This latter method 
is that now generally used, as by it the requisite steadiness of head 
or pressure can be secured. The closed type is subject to objec- 
tionable sudden changes of pressure which prevent or break 
uniform rates of filtration. The sand is supported upon a plat- 
form with a suitable system of pipes fitted with valves or gates 
for the withdrawal of the filtered water, the space below the 
platform forming a small sedimentation-chamber. They are 
usually constructed in comparatively small circular units, so that 
one or more of a group may be withdrawn from operation for 
the purposes of cleaning or repairs without interfering with the 
operation of the others. This system of small units, gives some 
marked practical advantages, as housing is readily accomplished, 
and if necessary the plant may be easily removed from one point 
to another. 

It is obvious that with the large amount of water forced 
through a given area of filter-bed the sand will become clogged 
within a comparatively short time, requiring washing and replac- 
ing. Mr. Fuller found at Cincinnati that the periods between 
washings when fine sand was used in the filters ranged from 8 to 



TYPES AND GENERAL ARRANGEMENT. 



317 



24 hours, with an average of 15, but with coarse sand the average 
became 20, with a range of from 6 to 36 hours. The time required 
for washing the sand at Cincinnati was 20 minutes for coarse or 
30 minutes for fine. At Providence Mr. Weston found that the 
average time of washing was about 11 minutes. The cleaning 
is accomphshed partially by stirring the sand with revolving 
arms, as shown in the accompanying figures, but generally by 




Continental Filter. 

forcing the water in a reverse direction through the sand and 
allowing the wash-water either to run to waste or to be again 
purified. The filters are designed for the purpose of cleaning 
by the reversal of the direction of the flow of water. Latterly 
the sand has been cleaned by forcing compressed air at a low 
pressure through it and the superimposed water. The passage of 
the air or water upward through the sand produces such a com- 
motion among the grains that they rub against each other and 



318 WATER-WORKS FOR CITIES AND TOWNS. 

clean themselves of the adhering material, allowing it to be car- 
ried off by the water above the sand. Both methods are much 
used and are satisfactorily effective for the purpose. 

It was found at Cincinnati that 4 to 9 per cent, with an average 
of 5 per cent, of filtered water was required for washing the fine 
sand, and only 2 to 6 per cent, with an average of 3 per cent, for 
the coarse sand of the mechanical filters used in Mr. Fuller's 
experiments. Mr. Weston has found about the same figures 
in his experimental work at Providence. The wash- water need 
not be wasted at all if it is pumped back into the subsidence-tanks. 

It has been found in some cases that the efficiency of the 
filters after washing is not quite normal, and that possibly 2 or 
3 per cent of the water must be wasted unless it is allowed to 
run back into the subsidence-tanks and again pass through the 
filter. Under such circumstances it has required 20 to 30 minutes 
of operation of the filter after washing to regain its normal effi- 
ciency. 

252. Cost of Mechanical Filters. — The cost of these mechani- 
cal filters has been found to range as high as a rate of $500,000 
per acre, which is probably about ten times as much as the rate 
of cost for the slow sand filters. On the other hand, the efficiency 
of the mechanical filters may be as high as the other class, with a 
rate of filtration from thirty to fifty times as great, and with a 
cost of operation less than that of the slow sand filters. The 
cost of the filters per million gallons of filtered water may, there- 
fore, be reduced to perhaps one fourth of that of the slow sand 
type. 

253. Relative Features of Slow and Rapid Filtration. — It is 
premature, even unnecessary, to make a comparison between 
the slow and rapid sand filters. The former are well adapted 
to a large class of potable waters in which there is not too much 
or too finely divided solid matter and in which the coloring from 
organic origin is not serious. They have the advantage of requir- 
ing no chemicals and are capable- of attaining a high degree of 
efficiency. The average rate of filtration may be taken about 
3,000,000 gallons per acre per day. The rapid sand filter, on the 
contrary, requires the application of a coagulant, but has thirty 
to fifty times the capacity of the other class. It is better adapted 



RELATIVE FEATURES OF SLOW AND RAPID FILTRATION. 319 

to the removal of turbidity and color, and when properly oper- 
ated it gives a high efficiency. A sufficiently extended experience 
has not yet, however, been attained to enable a complete state- 
ment to be made as to the entire field to which they may be 
adapted. They have certainly been shown to possess valuable 
qualities in a number of respects, and they are undoubtedly 
destined to play an important part in the purification of waters. 



PART IV. 

SOME FEATURES OF RAILROAD ENGINEERING. 



CHAPTER XXI. 

254. Introductory. — The first step toward the construction 
of a railroad is the location of the line, which requires as an initia- 
tive a careful ocular examination of the general vicinity of the 
proposed road, supplemented by simple and approximate instru- 
mental work rapidly performed. Following this reconnaissance, 
as it is called, more complete surveys and examinations are made 
both in the field and on the maps plotted from the data of the 
field-work. The prosecution of this series of operations produces 
the final location, together with the accumulation of such maps, 
profiles, and other data as may be required in the construction 
of the road-bed, bridges, and other structures constituting the 
complete railroad line with its ballast and track in place ready 
for traffic. 

The ultimate purpose of any railroad line is the transportation 
of passengers and freight under conditions, including those of a 
physical natu'^e connected with the road as well as the rates 
received, leading to profitable returns. Competition or other 
circumstances attending the traffic of a given road will fix the 
maximum rates to be charged for transportation. It is the 
business, first, of the civil engineer so to locate and design the 
road and, second, of the manager so to conduct the transportation 
as to make the margin of profits the greatest possible. It will 
be the purpose of this lecture to consider in a general way only 

320 



THE ROYAL GORGE. 



321 




The Royal Gorge. 



333 SOME FEATURES OF RAILROAD ENGINEERING. 

some of the features of a railroad and its operation which are 
related directly to civil engineering. 

255. Train Resistances. — It is a fact confirmed by constant 
daily experience that, however nicely the machine impelling the 
railroad train or the tracks supporting the cars may be built, 
considerable frictional and other resistance is offered to the move- 
ment of the train when the latter passes over a perfectly level and 
straight track. 

A considerable portion of the cost of transportation is ex- 
pended in overcoming this resistance. When the line fails to be 
either level or straight other resistances of magnitude are devel- 
oped ; they are called the resistances of grades and curves : and 
it is the business of the civil engineer so to design the railroad as 
to reduce these two classes of resistance to an absolute minimum, 
in view of certain other conditions which must be concurrently 
maintained. 

256. Grades. — The grade of a railroad is expressed usually 
in this country by the number of feet through which 100 feet of 
length of line rises or falls, or by some expression equivalent to 
that. If, for instance, the line rises 1.5 or 2 feet in 100, it is said 
to have an ascending grade of 1.5 or 2 per cent. Or if the line 
falls the same amount in the same length, it is said to have 
a descending grade of 1.5 or 2 per cent. It is evident that 
a grade which descends in one direction would be an ascend- 
ing grade for trains moving in the opposite direction, so 
that grades favoring traffic in one direction oppose it in the 
other. Hence, other things being equal, that road is the most 
advantageous for the movement of trains which has the least 
grade. The grades of railroads seldom exceed 2 or 2.5 per cent, 
although, as will presently be shown, there are some striking 
exceptions to that general observation. The actual angles of 
inclination of railroad tracks from a horizontal line are therefore 
as angles very small, but their disadvantages for traffic increase 
rapidly. 

A simple principle in mechanics shows that if the railroad 
train with a weight W moves up a 2 per cent grade, one com- 
ponent of the train weight acts directly against the tractive force 
of the locomotive or other motive power. If a is the angle of 



GRADES. 323 

inclination of the track to a horizontal line, this opposing com- 
ponent will have the value W sin a. When angles are small their 
sines are essentially equal to their tangents. Hence, in this 
case, sin a would have the value .02 or 1/50 of the train weight. 
If the weight of the train were 500 tons, which is a rather light 
train for the present time, this opposing force would be 10 tons, 
or 20,000 pounds, which, as we shall see later on, is more than 
one half of the total tractive force of any but the heaviest loco- 
motives built at the present day. This simple instance shows 
the advantage of keeping railroad grades down to the lowest 
practicable values. 

One of the most economical freight-carrying roads in the 
United States is the Lake Shore and Michigan Southern of the 
New York Central system, running from Buffalo to Chicago. Its 
maximum grade is 0.4 of i per cent. The maximum grade of 
the N. Y. C. & H. R. R. R. is 0.75 of i per cent between New 
York City and Albany and between Albany and Buffalo, 1.74 
per cent at Albany, i . 1 2 per cent at Schenectady, and i per cent 
at Batavia. Pushers or assistant locomotives are used for heavy 
trains at the three latter points. The maximum grade of the 
Pennsylvania R. R. on the famous Horseshoe Curve between 
Altoona and Cresson is 1.8 per cent. It is advantageous, where- 
ever practicable, to concentrate heavy grades within a short 
distance, as in the case of the New York Central at Albany, and 
use auxiliary engines, called pushers or assistants. Some of the 
heaviest grades used in this country are found on the trans-con- 
tinental lines where they pass the summits of the Rocky Moun- 
tains or the Sierras. In one portion of its line over a stretch of 
25.4 miles the Southern Pacific R. R. rises 2674 feet with a 
maximum grade of 2 . 2 per cent ; also approaching the Tehacipi 
Pass in California the maximum grade is about 2.4 per cent. 
At the Marshall Pass on the Denver & Rio Grande R. R. there 
is a rise of 3675 feet in 25 miles with a maximum grade of 4 per 
cent. The Central Pacific R. R. (now a part of the Southern 
Pacific system) rises 992 feet in 13 miles with a maximum grade 
of 2 per cent. The Northern Pacific R. R. rises at one place 
1668 feet in an air-line distance of 13 miles with a maximum grade 
of 2.2 per cent. Probably the heaviest grade in the world on an 



324 SOME FEATURES OF RAILROAD ENGINEERING. 

ordinary steam railroad is that of the Calumet Mine branch of 
the Denver & Rio Grande R. R., which makes an elevation of 2700 
feet in 7 miles on an 8 per cent grade and with 25° curves as 
maximum curvature. These instances are sufficient to illustrate 
maximum railroad grades found in the United States. 

257. Curves. — Civil engineers in different parts of the world 
have rather peculiar classifications of curves. In this country 
the railroad curve is indicated by the number of degrees in it 
which subtend a chord 100 feet in length. Evidently the smaller 
the radius or the sharper the curvature the greater will be the 
number of degrees between the radii drawn from the centre of 
a circle to the extreniities of a loo-feet chord. American civil 
engineers use this system for the reason that the usual tape or 
chain used in railroad surveying is 100 feet long. A very simple 
and elementary trigonometric analysis shows that under this 
system the radius of any curve will be equal to 50 divided by 
the sine of one half of the angle between the two radii drawn 
to the extremities of the loo-feet chord. In other words, it is 
equal to 50 divided by the sine of one half the degree of curva- 
ture. The application of this simple formula will give the fol- 
lowing tabular values of the radii for the curves indicated: 

Curve. Radius in Feet. 

1° 5729-65 

2'^ 2864.93 

3° 1 9 1.0. 08 

4° 1432-69 

5° 1146.28 

6° 955-36 

7° 819.02 

.8° 716.78 

9° 637.27 

10° 573-69 

12° 478-74 

15° 383-06 

20° 287 .91 

258. Resistance of Curves and Compensation in Grades. — In- 
asmuch as the resistance oft'ered to hauling the train around a 



TRANSITION CURVES. 325 

curve increases quite rapidly as the radius of curvature decreases, 
it is obvious that in constructing a railroad the degree of each 
curve should be kept as low as practicable, and that there should 
be no more curves than necessary. While no definite rule can 
be given as to such matters, curves as sharp as io° (573.69 feet 
radius) should be avoided wherever practicable. It is not ad- 
visable to run trains at the highest attainable speeds around such 
curves, nor is it done. Inasmuch as curve resistance has consid- 
erable magnitude, as well as the resistance of grades, it is natural 
that wherever curves occur grades should be less than would be 
permissible on straight lines or, as they are called, tangents. If a 
maximum gradient is prescribed in the construction of a railroad, 
that gradient will determine the maximum weight of train which 
can be hauled on the straight portions or tangents of the road. 
If one of these grades should occur on a curve, a less weight of 
train could be handled by the same engine than on a tangent. 
Hence it is customary to reduce grades by a small amount for 
each degree of curvature of a curve. This operation of modi- 
fying the grades on curves so as to enable a locomotive to haul 
the same train around them as up the maximum grade on a tan- 
gent is called compensating the curves for grade. There is no 
regular rule prescribed for this purpose, because the combination 
may necessarily vary between rather wide limits in view of speed, 
condition of track, and other influencing elements. The com- 
pensation, however, has perhaps frequently been taken as lying 
between .03 and .05 per cent of grade for each degree of curva- 
ture. In other words, for a 5° curve the grade would be .15 
to .25 per cent less than on a tangent. This compensation for 
grades is carefully considered in each case by civil engineers in 
view of experience and such data as special investigations and 
general railroad operation have shown to be expedient. 

259. Transition Curves. — High speeds for which modem rail- 
roads are constructed have made it necessary not only to protect 
road-beds, but also to make the passage from tangents to curves 
as easy and smooth as possible. This is accomplished by intro- 
ducing between the curve and the tangent at each end what is 
called a "transition" curve. This is a compound curve, i.e., a 
curve with varying radius. At the point where the tangent or 



326 



SOME FEATURES OF RAILROAD ENGINEERING. 







I^V p V. v/^ 



;s 



-e,s- 



,e,8- 



ROAD-BED, INCLUDING TIES. 



327 



straight line ceases the radius of the transition curve is infinitely 
great, and it is gradually reduced to the radius of the actual 
curve at the point where it meets the latter. By means of such 
gradual change of curvature the trucks of a rapidly moving 
train do not suddenly pass from the tangent to the curve proper, 
but they pass gradually from motion in a straight line to the 
sharpest curvature over the transition curve. The rate of transi- 
tion is fixed by the character of the curves, which have been sub- 
jected to careful analysis by civil engineers, and they can be 
found fully discussed in standard works on railroad location. 

260. Road-bed, including Ties. — Not only the high rates of 
speed of modern railroad trains but the great weights of locomo- 
tives and cars have demanded a remarkable degree of perfection 
in the construction of the road-bed and in the manufacture of 
rails. The favorite ballast at the present time for the best types 
of road-beds is generally broken stone, although gravel is used. 
The first requisites are a solid foundation and perfect drainage 
whether in cuts or fills. Figs. 1,2,3, and 4 show two or three types 
of road-bed used by the New York Central and Hudson River 
R. R., the Pennsylvania R. R., and a special type adopted by the 
B. & O. for the belt-line tunnel at Baltimore. These sections 
show all main dimensions and the provision made for drainage. 
The general depth of ballast is about 18 inches, including the 
drainage layer at the bottom. The total width of road-bed for a 
double-track line varies frequently between 24 and 25 feet, while 
the width of a single-track line maybe found between 13 and 14 
feet. In the cross-sections shown the requirements for drainage 




Stone Draia Brick Drain 

Fig. 4.— Baltimore Belt-line Tunnel, B. & O. Ry. 

are found to be admirably met. Timber ties are almost invaria- 
bly used at the present time in this country, although some experi- 
mental steel ties have been laid at various points. Fig. 5 shows 



328 



SOME FEATURES OF RAILROAD ENGINEERING. 



the steel tie adopted for experiment on the N. Y. C. & H. R. R. R. 
within the city hniits of New York. The time will undoubtedly 
come when some substitute for timber must be found, but the 



Gage-l-SJiJ- 




FiG. 5. 

additional cost of steel ties at the present time does not indicate 
their early adoption. 

261. Mountain Locations of Railroad Lines. — The skill of the 
civil engineer is sometimes seve ely taxed in making mountain 
locations of railroads. Probably no more skilful engineering 




SWITCHBACKS ON THE LINE , 

OF THE 

LIMA AND OROYA RAILWAY IN PERU. 



Fig. 6. 
work of this kind has ever been done than in the crossings of the 
Rocky Mountains and the Sierras in this country by trans-con- 
tinental railroad lines, although more striking examples of railroad 
location for short distances may perhaps be found in Europe or 
other countries. The main problem in such cases is the making 



MOUNTAIN LOCATIONS OF RAILROAD LINES. 



329 



of distance in order to attain a desired elevation without exceed- 
ing maximum grades, such as those which have already been 
given. ]\Iost interesting engineering expedients must sometimes 
be resorted to. One of the oldest of these is the switchback 
plan shown in Fig. 6. This is probably the simplest procedure 
in order to make distance in attaining elevation. The line is 




Canon of the Rio Las Animas, near Rockwood. 

run up the side of a mountain at its maximum grade as far in 
one direction as it may be desirable to go. It then runs back 
on itself a short distance before being diverted so as to pass up 
another grade in the reverse direction. This zigzagging of 
alignment may obviously be made to attain any desired elevation 
and so overcome the summit of a mountain range. The old 
switchback coal road near Mauch Chunk, Pa., is one of the oldest 
and more famous instances of the method, which has many times 
been employed in other locations. 



330 



SOME FEATURES OF RAILROAD ENGINEERING. 




THE GEORGETOWN LOOP— TUNNEL-LOOPS. 331 

A more striking method, perhaps, is that of loops by which the 
direction of a hne or motion of a train on it is continuous. Dis- 
tance is made by a judicious use of the topography of the locaHty 
so as to run the Hne as far up the side of the valley as practicable 
and then turn as much as a semicircle or more, sometimes over 
a bridge structure and sometimes in tunnel, so as to give further 
elevation by running either on the opposite side of the valley 
or on the same. A succession of loops or other curves suitably 
located will give the distance desired in order to reach the sum- 
mit. 

262. The Georgetown Loop. — Fig. 7 shows one of these spiral 
or loop locations on the Georgetown branch of the Union Pacific 
Railroad in Colorado. It is a well-known and prominent instance 
of railroad location of this kind. On the higher portion of this 
loop system included in the figure there is a viaduct on a curve 
which crosses the line 75 feet above the rail below it and 90 feet 
above the water. This location is a specimen of excellent railroad 
engineering. The length of line shown in the figure, including 
the spiral, is 8^ miles, and it cost $265,000 per mile exclusive of 
the bridges. 

263. Tunnel-loop Location, Rhaetian Railways, Switzerland. — 
In Figs. 8 and 9 are shown two portions of the Albula branch of 
the Rhaetian Railways, Canton Graubiinden, southeastern Swit- 
zerland. The line connects the valleys of the Albula and the 
Inn, the former being one of the branches of the Rhine and the 
latter of the Danube; it therefore cuts the divide between the 
watersheds of those two rivers. It is a 3.28-feet gauge single- 
track road, and is built largely for tourist traffic, as the scenic 
properties of the line are remarkable. 

The maximum grade on this line is 3.5 per cent. Over one 
portion of the line 7.8 miles long one third of that distance is in 
tunnel and 1 5 per cent of it on viaducts. The radii of the centre 
1 nes of the tunnels are 460 and 394 feet, while the lengths of the 
tunnels range from 1591 to 2250 feet, with a maximum grade 
in them of 3 per cent. The weight of rails used is 50 pounds per 
yard on grades of 2.5 per cent or less, but for heavier grades 55- 
pound rails are employed. The cross- ties are of mild steel and 
weigh 80 pounds each except in the long xVlbula tunnel, where 



332 SOME FEATURES OF RAILROAD ENGINEERING. 




TUNNEL-LOOP LOCATION. 



333 














l4 



% 






334 SOME FEATURES OF RAILROAD ENGINEERING. 

treated oak ties are used as being better adapted to the special 
conditions existing there. It will be observed that in each case 
the line rises from the left-hand portion of the figure toward the 
right. 

The tunnels are represented by broken lines, and they are in 
every instance on circular curves. Fig. 9 represents the line 
running from a point on the east side of the Albula River through 
a heavy cut and then across the valley of the Albula into a tunnel 
2250 feet long. The line then runs chiefly in cuts to a point where 
there are two tunnels, one over the other; indeed the line over- 
laps itself in loops and tunnels a number of times in that vicinity. 
That portion of the road shown in Fig. 8 is less remarkable than 
the other, although it exhibits extraordinary alignment. This 
example of railroad location is one of the most striking among 
those yet completed. It would appear to indicate that no topo- 
graphical difficulties are too great to be overcome by the civil 
engineer in railroad location in a most rugged and precipitous 
country. Obviously such a line could not be economically 
operated for heavy freight traffic. 

Railroad lines frequently lead through mountainous regions 
affording some of the grandest scenery in the world accessible 
to the travelling public. In this country the Canadian Pacific, 
the Northern Pacific, the Great Northern, and the Rio Grande 
Western probably exhibit the most remarkable instances of this 
kind. 



CHAPTER XXIT. 

264. Railroad Signalling. — The birth of the art of railroad 
signalHng was probably coexistent with that of the railroad. 
At the very outset of the movement of railroad trains it became 
imperative to insure to a given train the sole use of the single 
track at schedule periods. Both head-to-head and rear-end colli- 
sions were liable to occur on main tracTcs, as well as false meetings 
at branches and cross-overs. 

265. The Pilot Guard. — One of the earliest if not the earliest of 
systematic procedures in England to accomplish the safe use of a 
railroad track involved the employment of the ' ' pilot guard ' ' on 
single-track roads. The pilot was an employe whose duty it 
was to accompany every tra n over a stated section of the line. 
The authority to start trains was lodged in him. When it became 
necessary to start two or three trains from the same point and in 
the same direction, it was also his duty to issue to each train con- 
ductor what was called a pilot ticke , equivalent to a modern 
train order to run the train over the section under his control. 
In that case he was obliged to accompany the last train to the 
other end of his section, and no more trains could move over that 
section in the same direction until his return to his first station. 
As no train could pass over the section without either him or his 
pilot ticket, it is clear that the system could prevent head-to-head 
collisions, but in itself it is not sufficient to eliminate rear-end 
colHsions. This system is still employed in Great Britain on 
some short branch lines. 

266. The Train Staff. — Another method nearly as old as the 
preceding is that of the train staff, used in an improved form at 
the present time on some single-track roads. No train under 
this system can pass over any given section of the line unless it 
carries the staff belonging to that section, the staff being a piece 

335 



336 SOME FEATURES OF RAILROAD ENGINEERING. 

of wood or metal i to i^ inches in diameter and i8 to 20 inches 
long. In order to cover the case of two or more trains starting in 
the same direction at one end of a section before running a train 
in the opposite direction, tickets were issued, the staff being taken 
by the last train. The proper operation of this method, like 
that of the preceding, would prevent head-to-head collisions, 
but is not sufficient in itself to prevent one train running into the 
rear of another while both are proceeding in the same direction 
in the same section. 

267. First Basis of Railroad Signalling. — These and other 
similar systems answered fairly well the more simple require- 
ments of early railroad operation. Strictly speaking they are 
not methods of signalling, although it may be said that each 
train is a signal in itself. With the development of railroad 
business it was found that other methods better adapted to a 
more efficient and rapid movement of trains were imperative. 
It was in response to the advancing requirements of the railroad 
business that the first approach to what is now so well known 
as the block system of signalling was made in 1842. An EngHsh 
engineer, subsequently, Sir W. F. Cooke, stated the following 
sound principles as to the basis of efficient railroad signalling : 

' ' Every point of a line is a dangerous point which ought to be 
covered by signals. The whole distance ought to be divided 
into sections, and at the end as well as at the beginning of them 
there ought to be a signal, by means of which the entrance to the 
section is open to each train when we are sure that it is free. 
As these sections are too long to be worked by a traction rod, 
they ought to be worked by electricity." 

The main features of railroad signalling, as thus set forth, 
have continued to characterize the development of the block 
system from that early day to the present. The electrical appH- 
cation to which reference is made in the preceding quotation 
was that of the needle, which by its varying position could indi- 
cate either " line clear" or " line blocked." In 185 1 electric bells 
were used in railroad signalling on the Southeastern Railway of 
England. Various other developments were completed from 
time to time in Great Britain until the Sykes system of block 
signalling was patented in 1875. One of the main features of 



CODE OF AMERICAN RAILWAY ASSOCIATION. 337 

the system, and perhaps the most prominent, was the control of 
the track signals at the entrance end of the block by the signalman 
at the advance end. He exerted this control by electrically 
operated locks. About 1876 the Pennsylvania Railroad intro- 
duced the block system into the United States, which has 
since been greatly developed in a number of different forms, and 
its use has been widely extended over many if not most of the 
great railroad systems of the country. It is not only used for 
the movement of trains, but also for the protection of such special 
danger-points as switches, cross-overs, junctions, drawbridges, 
heavy descending grades, sharp curves, and other points needing 
the protection which a well-designed block system affords. 

268. Code of American Railway Association. — The code of the 
American Railway Association gives the following definitions 
among others pertaining to the block system: 

Block. — A length of track of defined limits, the use of which 
by trains is controlled by block signals. 

Block Station. — The office from which block signals are oper- 
ated. 

Block Signal. — A fixed signal controlling the use of a block. 

Home Block Signal. — A fixed signal at the entrance of a block 
to control trains in entering and using said block. 

Distant Block Signal. — A fixed signal of distinctive character 
used in connection with a home block signal to regulate the 
approach thereto. 

Advance Block Signal. — A fixed signal placed in advance of a 
home block signal to provide a supplementary block between 
the home block signal and the advance block signal. 

Block System. — A series of consecutive blocks controlled by 
block signals. 

Telegraph Block System. — One in which the signals are oper- 
ated manually upon telegraphic information. 

Controlled Manual Block System. — One in which the signals 
are operated manually, and by its construction requires the co- 
operation of a signalman at both ends of the block to display a 
clear signal. 

Automatic Block System. — One in which the signals are oper- 



338 SOME FEATURES OF RAILROAD ENGINEERING. 

ated by electric, pneumatic, or other agency, actuated by a train 
or by certain conditions affecting the use of a block. 

268a. The Block. — It is seen by these definitions that what 
may be called the unit in railroad signalling is the "block"; it 
may be of almost any length from a few hundred feet to 6 or 8 
miles, or even more. On a single-track railroad it may evidently 
extend from one side track or passing-place to another. Over 
portions of lines carrying heavy traffic it may be a half-mile or 
less. The length of block will depend, then, upon the intensity 
and kind of traffic, the physical features of the line, such as curva- 
ture, grade, sidings, cross-overs, and other similar features, the 
location, whether in cities, towns, or open country, as well as upon 
other elements aft'ecting conditions of operation which it is desir- 
able to attain. 

269. Three Classes of Railroad Signals — The Disc. — The sig- 
nals used in railroad operation may mainly be divided into three 
classes: semaphores, banners, and discs. In general -they may 
convey information by form, position, and color. The disc is 
used by causing it to appear and disappear before an aperture, 
usually a little larger than itself, in a case standing perhaps 10 
or 12 feet high alongside the track, and is admirably typified 
in the Hall electric signal. On account of its shape, the case 
in which the disc is operated is frequently called the banjo, as 
it is quite similar in shape to that musical instrument placed in 
a vertical position, the key end resting on the ground. 

270. The Banner Signal. — The banner signal is usually oper- 
ated by rotation about a ver ical axis, frequently in connection 
with switches. Its full face painted red, exposed with its plane 
at right angles to the track, indicates ' ' danger " or ' ' stop." With 
its face turned parallel to the track, showing only its edge to 
approaching trains, a ' ' clear " lin or ' ' safety " is indicated. 

In the present development of railroad signalling the banner 
and disc patterns have a comparatively limited application, 
although, on the whole, they are largely used. The banner 
signal is mostly employed in the manual operation of switches, 
turn-outs, and cross-overs, and for other local purposes, partic- 
ularly on lines of light traffic. 



THE SEMAPHORE. 



339 




Fig. io. — Semaphore Signals. 



340 



SOME FEATURES OF RAILROAD ENGINEERING. 



271. The Semaphore. — The semaphore is now mainly used in 
connection with block signalling. Like many other appliances 
in railroad signalling it was first used in England, by Mr. C. H. 
Gregory, about 1841. Its name is derived from the combination 
of two Greek words signifying a sign-bearer. It consists of a 
post varying in height from about 3 to 35 or 40 feet, carrying 
an arm at its top from 3 to 5 feet long, pivoted within a foot or 
18 inches of one end, the long end suitably shaped and painted 
and the other arranged with a lens so that when operated at night 
in connection with a lamp it may exhibit a properly colored light. 
The post of the semaphore is placed alongside the track so as to 
be on the right-hand side of an approaching train, the long arm 
rising and falling as a signal away from the track and in a plane 
at right angles to it. The other arm of the semaphore signal 




Semaphore on Pennsylvania Railroad. 

may be connected by wires or rods and light chains running 
over pulleys with suitable levers and weights operated either in a 
near-by signal cabin or by a signalman stationed near the sema- 
phore itself; or it may be operated by electric or pneumatic 
power, as in many of the later installations. The semaphore 
may, therefore, be operated at the post or by suitable appliances 
at a distance. 

272. Colors for Signalling. — The colors used either for painted 
signals for daylight exposure or for coloring lenses for night 
signalling are red, white, and green, as ordinarily employed in 
this country; red signifying " danger " or "stop," white signify- 



INDICATIONS OF THE SEMAPHORE. 341 

ing " safety " or " clear track," and green signifying " caution " 
or ' ' proceed with train under control," indicating that a train may 
go forward cautiously, expecting to find an obstruction or occupied 
track. In England green is largely employed to indicate ' ' safety ' ' 
or ' ' clear track," on the ground that a white light is so similar to 
any other in its vicinity that the latter may too easily be mis- 
taken for a signal. While there is some diversity of views in 
this country on that point, the consensus of engineering opinion 
seems to favor the retention of the white for the track safety 
signal. 

273. Indications of the Semaphore. — It is evident that a sema- 
phore affords facilities of form, position, and color in its use for 
the purpose of signalling. The horizontal position is the most 
striking for the semaphore arm, as it then extends at right angles 
to the post and to the right or away from the track ; this position 
is, therefore, taken to indicate "danger" or stop." No train 
may, therefore, proceed against a horizontal semaphore arm. 

It might at first sight appear that the vertical position of 
the semaphore arm close against the post could be taken to indi- 
cate "safety" or "clear track" or "proceed," but experience 
has shown that such a position may be injudicious, except under 
special conditions where it has lately been employed to make 
that indication. If the semaphore arm should be knocked or 
blown from the ordinary post, the engineman of an approaching 
train probably would not be able to detect the actual condition 
of things and might accept the appearance of the semaphore 
as indicating a clear line, thus justifying himself in proceeding 
at full speed, while the signalman in his cabin might have placed 
the signal at ' ' danger." A position of the semaphore arm, there- 
fore, at an angle of 65° or 70° below the horizontal is usually 
taken as a safety signal. This position is in marked contrast 
to the horizontal arm and at the same time makes the absence of 
the semaphore arm impossible without immediate detection from 
an approaching locomotive. After dark the semaphore in a 
position of danger exhibits a red light through the lens in its 
short arm when the long arm is at the "danger" position or 
horizontal. Similarly, when the long arm is in the safety position 
a white light is exhibited through the lens in the shorter arm, 



342 SOME FEATURES OF RAILROAD ENGINEERING. 

SO that the respective conditions of clear or obstructed track 
are made evident to the engineman as well by night as by day 
on his approach to the semaphore. 

In some of the latest signal work three positions of the sema- 
phore arm on one post, known as three-position block signalling, 
have been employed. In this system a special post, frequently 
on a signal bridge over the track, permits the vertical position 
of the semaphore arm to indicate ' ' clear track, ' ' while the diagonal 
or inclined position below the horizontal indicates "caution." 
In the Mozier three-pcsition signal a diagonal or inclined position 
above the horizontal indicates ' ' caution ' ' an addition to the two 
usual positions of ' ' stop " and ' ' clear." 

These are the elements, so to speak, of railroad signalling at 
the present day. They are combined with various appliances 
and in various sequences, so as to express all the varied condi- 
tions of the track structure which affect the operation of the 
road or the movement of trains upon it. These combinations 
and the appliances employed in them are more or less involved 
in their principal features and complicated in their details, 
although the main principles and salient points are simple and 
may easily be exhibited as to their mode of operation and general 
results. In this treatment of the subject it will only be possible 
to accomplish these general purposes without attempting to set 
forth the mechanical details by which the main purposes of 
railroad signalling are accomplished. 

274. General Character of Block System. — It is evident from 
what has already been stated that the block system of signalling 
involves the use of fixed signals located so as to convey promptly 
to approaching trains certain information as to the condition 
of points of danger approached. Furthermore, this system of 
signals is designed and operated on the assumption that every 
point is to be considered as a danger-point until information is 
given that a condition of safety exists. The usual position of 
signals, or what may be called the normal position, is that of 
"danger," and no position of "safety" is to be given to any 
signal except to permit a train to pass into a block whose con- 
dition of safety or clear track is absolutely assured. These are 
the ground principles on which the signal systems to be con- 



BLOCK SYSTEMS IN USE. 343 

sidered are designed and operated, although there are some 
conditions under which the normal signal position may be that 
of safety. 

275. Block Systems in Use. — The block systems now in general 
use are:. 

The IManual, in which the signals at each end of each block 
are wholly controlled and operated by the signalman at each 
signal point. 

The Controlled-Manual, in which the signals at the entrance 
to each block are controlled either electrically or in some other 
manner by the signalman at the other extremity of that block, 
but are operated subject to that control by the signalman at the 
entrance of the block. 

The Auto-Manual, in which the signals are generally operated 
and controlled as in the Manual or Controlled-Manual, except 
that they are automatically returned to the danger position as 
the rear car of a moving train passes them. 

The Automatic, in which the operation of the signals is wholly 
automatic and generally by electricity, or by a combination of 
electric and pneumatic mechanism. In this system no signal- 
men are required. 

The Machine, which is a controlled block system for single- 
track operation and in which machines operated electrically 
with detachable parts, as staffs, are employed in connection with 
other fixed signals alongside the track. 

The main features of these various systems of blocking are, 
in respect to their signalling, the same, but the means for actuat- 
ing or manipulating the signals and the conditions under which 
moving tra ns receive the necessary instructions are different. 
They all have the same main objects in view of improving rail- 
road operation by enhancing both safety and facility of train 
movement. 

"Absolute" blocking is that system of block signalling which 
absolutely prevents one train passing into a block until the pre- 
ceding train is entirely out of it, or, in other w^ords, until the block 
is absolutely clear. 

Permissive ' ' blocking is, strictly speaking, the violation of 
the true block system of signalling, since under it a train may 



344 SOME FEATURES OF RAILROAD ENGINEERING. 

under certain precautionary conditions enter a block before the 
preceding train has passed out of it. 

276. Locations of Signals. — In proceeding to locate signals 
along a railroad line it is imperative to recognize the preceding 
purposes as controlling motives. Signals must be seen readily 
.and clearly in order to be of the greatest service to the enginemen 
of approaching trains, and their positions must be selected with 
that end in view. Locations of switches, cross-overs, junctions, 
and other similar track features will control the locations of the 
signals which are to protect them. The main or home signal in 
these special cases may usually be placed from 50 to 200 feet 
from the point which is to be governed, the so-called ' ' distant" 
signal being placed about 2000 feet for level track back of the 
main or home signal. 

277. Home, Distant, and Advance Signals. — A complete sys- 
tem of signals employed in blocking includes first of all the so- 
called "home" signal at each extremity of a block, then at a 
distance of 2000 to 2500 feet back from the home signal is placed 
the ' ' distant" signal. The latter is thus approached and passed 
before reaching the home signal. On the other side of the * ' home " 
signal at least a maximum train length into a block about to be 
entered by a moving train is placed the ' ' advance" signal. The 
distance of the advance signal from the home signal may be 1500 
to 2500 feet. As a moving train approaches the end of a block 
it first meets the distant signal, the purpose of which is to indi- 
cate what the engineman may expect to find at the home signal. 
If the distant signal is in the danger position, he will pass it with 
caution and place his train under control so as to be able to stop 
at the home signal. If he finds the distant signal in a safety 
position, indicating the same position of the home signal, he 
may approach the latter without reducing speed, confident that 
the next section is clear and ready for him. The advance signal 
forms a kind of secondary or supplementary block into which 
the train, under certain conditions, may enter when the block 
in which it is found is obstructed, but no train may pass the 
advance signal unless the entire block is clear except when, under 
permissive working, the train proceeds with caution, expecting 
to find the track either obstructed or occupied. This group 



TYPICAL WORKING OF AUTO-CONTROLLED MANUAL SYSTEM. 345 

of three signals — the distant, the home, and the advance — taken 
in the order in which the moving train finds them, is located at 
each extremity of the block. Although the home signal is said 
to control the movement of trains in a block at the entrance to 
which it is found, as a matter of fact it appears that the advance 
signal in the final event holds that control. 

278. Typical Working of Auto-Controlled Manual System. — 
The mode of employing these signals can be illustrated in a 
typical way by the diagrams. Figs. 11, 12, and 13, which exhibit 
in a skeleton manner Pattenall's improved Sykes system which 
belongs to the Auto-Controlled Manual class. In these figures 
the end of block i , the whole of blocks 2 and 3 , and the beginning 
of block 4 are shown. Stations A, B, and C indicate the ex- 
tremities of blocks. The signals 5, 5', and S" are the home sig- 
nals, while D, D' , and D" indicate distant signals, and A, A', 
and A" advance signals. As the diagrams indicate, the stretch 
of double-track road is represented with east- and west-bound 
tracks. In order to simplify the diagrams, signals and stations 
are shown for one track only; they would simply be duplicated 
for the other track. The signal cabin is supposed to be located 
at each station, and at that cabin are found the levers and other 
appliances for working the signals operated there, the signals 
themselves being exposed alongside the track. In each signal 
cabin there is an indicator, as shown at /, /', and /". On the 
face of each indicator there are two slots, shown opposite the 
lines E and F. In the upper of these slots appears either the 
word "Clear" or "Blocked." In the lower slot appears 
either the word "Passed" or "On." The significance of these 
words will appear presently. On this indicator face at P, P', 
and P" are located electric push-buttons called plungers. The 
operation of the levers indicated at L, the counterweights d, and 
the locking detail / are evident from an inspection of the figure, 
and need no special explanation. It is only necessary to state 
that the locking-device / holds the bar be until it is released at 
the proper time, and that the counterweight may then return the 
lever from its extreme leftward position to that at the extreme 
right, at the same time placing the semaphore arm 5 in the posi- 
tion of danger. It is particularly important to bear in mind 



346 SOME FEATURES OF RAILROAD ENGINEERING. 




■di--ZZ 






TYPICAL WORKING OF AUTO-CONTROLLED MANUAL SYSTEM. 347 

this last observation. The counterweight is the feature of the 
system which always holds the semaphore arm in the position 
of danger, making that its normal position, except when it is 
put to safety for the passing of a train. 

If a westward train is represented in Fig. 1 1 at T as approach- 
ing station A to enter the block 2, both the distant signal D and 
the home signal 5 being at danger, the system is so arranged that 
the signalman at station A cannot change those signals, i.e., to a 
position of safety, until the signalman at station B permits him 
to do so. If the signalman at station A desires to open block 2 
for the entrance of the train T, he asks the signalman at station B 
by wire to release the lock / to enable him to do so. If there is 
no train in block 2, the signalman at station B pushes the button 
P' or "plunges" it. This raises the lock / at station A and the 
signalman immediately pulls the lever L to its extreme leftward 
position, throwing both the signals 5 and D to the position of 
safety or clear ^ indicated by the dotted lines at 5^ At the same 
time the indicator E at station A shows the words ' ' Clear to B," 
while the slot F' at B shows the words "On from A." The signals 
at stations B and C are supposed to be in their normal position 
of danger, and the indicator £' at station B shows the words 
"Blocked to C." The home and distant signals 5' and D' are 
now at danger, but the train T may enter block 2 and proceeds 
to do so, it being remembered that the signalman at station A 
cannot move the lever L, as it has passed out of his control ; not 
even the signalman at station B can give him power to do so. 
The train T now passes station A into block 2. As the last car 
passes over the point G its wheels strike what is called a track- 
treadle, an appliance having electrical connection with the lock /. 
The effect of the wheels of the last car of the train passing over 
the treadle at G is to release lock /, enabling the signalman at 
station A immediately to raise the arms 5 and D to the position 
of danger. It is to be observed that he cannot do this until the 
entire train has passed into block 2 ; nor, since his plunger is locked 
by the same treadle at G, can he signal ' ' Safety" or ' ' Clear" to 
the entrance of block i. Hence no train can enter block i to 
collide with the rear end of the train just entering block 2 . When 
the signalman at station A has raised his signal 5 to danger, it 



348 SOME FEATURES OF RAILROAD ENGINEERING. 

again passes out of his control, indeed out of both his control 
and that of the signalman at B, until the last car of the train 
passes over the treadle G' at the entrance of block 3. 

The train has now passed into block 2 and is approaching 
station B. The signalman at B asks C by wire to release the 
lever L', and if block 3 is clear, C plunges at P" . 

C then throws his lever L' so as to place the home and distant 
signals S' and D' at safety. The condition of things will then 
be shown by Fig. 12. As soon as the last car of the train has 
passed over the treadle at G' his lever U will be released and 
he can then throw the lever to the danger position, raising the 
home and distant signals S' and D' to the horizontal. After 
the danger position is assumed by the home signal S' , as well as 
the distant signal D' , he has no power over them until the signal- 
man at station C confers it on him by plunging the button P" . 

While the train has been in block 2 , the indicator /' has shown 
* ' Blocked to C" and ' ' Train on from A ," but as the train passes 
B the indicator reads "Blocked to C" and "Train passed from 
A," while the indicator /" at C reads "Blocked to .D" and 
"Train on from 5." This condition of the signals and trains 
is shown by Fig. 13. Also, when the last car passes over the 
treadle G' , but not till then, B may permit A to admit a train 
to enter block 2 should A so desire. Finally, when the train 
approaches C, the signalman at that point asks D to enable him 
to permit the train to enter block 4, and C confers the power by 
plunging if that block is clear. Fig. 13 exhibits the corresponding 
signals at C. 

This sequence of operations is typical of what takes place in 
this particular block-signal system at the limits of every succes- 
sive block, and differs only in details characteristic of this sys- 
tem from those which are performed in any other block-signal 
system.. 

279. General Results. — It is seen first that no signalman can 
operate a signal until the condition in the block ahead of him 
is such as to make it proper for him to do so, and then he can 
only indicate what is necessary for the safe entrance of the train 
into that block. Furthermore, immediately on the passage of 
the train past his home signal he must put the latter to danger 



DISTANT SIGNALS. 349 

or the counterweight may do it for him, the train itself when 
in a safe position having conferred the requisite power upon him. 
The signalman at the advance end of the block always knows 
when the train is about to enter it, for he is obliged to give his 
permission for that entrance. His indicator shows this result, 
and will continue to show it until the train passes out of the block. 
It is to be observed that the upper openings marked E on the 
indicator give information of the condition of the block in ad- 
vance, while the lower openings give information of the block 
in the rear. 

It is particularly important to notice that after the signal- 
man at the advance end of a block has "plunged" his plunger 
remains locked and it cannot be released until the train admitted 
to the block covered by the plunger has comple;ely passed out 
of that block, pei-mitting the track-treadle at the entrance to the 
next block to unlock the plunger. This feature makes it impossi- 
ble for one train to enter a block until the preceding train has 
passed out of it. 

If the permissive system of using a block be employed, in 
which the train is permitted to enter that block before a pre- 
ceding train leaves it, the treadle gives no protection against a 
rear-end collision with the first train. In such an exigency 
other devices must be used or the following train must proceed 
cautiously, expecting to find the track occupied. 

280. Distant Signals. — Thus far the distant signals have been 
treated incidentally only. They may be operated concurrently 
with or independently of the home signal in such a way that if 
danger is indicated, the distant signal gives its indication prior 
to that of the home signal. In this manner protection is given 
to the rear of a train approaching a block against the home signal 
set at "danger." After the obstruction is removed and the block 
cleared, the home signal is set at "safety" before the distant 
signal is cleared. 

281. Function of Advance Signals. — The advance signals are 
used when for any purpose it is desired to form a short block in a 
regular block. If, for instance, block 3 in Fig. 1 1 were obstructed 
by a train stopped by some failure of a locomotive detail, a train 
approaching station B in section 2 against the home signal 5' 



350 



SOME FEATURES OF RAILROAD ENGINEERING. 



set at ' ' danger" would be obliged to stop before entering block 3. 
It might then be permitted to enter the latter block, to be stopped 
by the advance signal A' set at "danger" or under instructions 
to pass it cautiously, expecting to find the track obstructed. 
It is thus seen that the advance signal creates what may be called 
an emergency block, and in reality finally controls the movement 
of trains in the block in which it is located. It would never be 
cleared unless the home signal were first cleared, nor would it be 
set at ' ' danger" unless the home signal gave the same indication. 

The preceding operation of the block system' of signalling con- 
trols the movement of trains along a double-track line. 

282. Signalling at a Single-track Crossing. — A somewhat simi- 
lar sequence of signal operations controls train movements at a 
crossing, whether single- or double-track. Fig. 14 illustrates the 




Fig. 14. 

use of signals required for the safe movement of trains at a single- 
track railroad crossing, which is supposed to be that of a north- 
and-south line crossing obliquely an east-and-west line. Precisely 
the same arrangement of signals operated in the same manner 
would be required if the crossing were at the angle of 90°. The 
signal cabin is placed, as shown, as near as practicable to the 
actual intersection of tracks. Trains may pass in either direction 
on either track, but in every case they would be governed by 
the signals at the right-hand side of the track as seen by the 
engineman. There will therefore be a set of signals on both 
sides of each track, each set governing the movement of trains 



SIGNALLING AT A SINGLE-TRACK CROSSING. 351 

in its own direction. Each home signal may be placed about 350 
feet from the actual intersection, and each distant signal 1200 to 
1500 feet from the home signal, or 1550 feet to 1800 feet from the 
intersection. Each advance signal must be at least as far in 
advance of the home signal as the maximum length of train, 
since it may be used to stop a train, the rear car of which should 
completely pass the home signal. In their normal positions 
every home signal should be set at ' ' danger, ' ' carrying with 
them the distant signals giving the same indication. The advance 
signals must also indicate -'danger" with the home signal. No 
train can then pass the crossing until the home and distant sig- 
nals indicate a clear line for it, the other signals at the crossing, 
except possibly the advance signal, being set at ' ' danger." If for 
any reason it is desired to hold the train after it is entirely free of 
the crossing, the advance signal would also indicate ' ' danger. ' ' 
It is thus seen that if the signals are properly set and obeyed, 
it is impossibl for two trains to attempt a crossing at the same 
time. It is not an uncommon occurrence, however, for an engine- 
man to run his train against th danger signal, and in order to 
make it impossible for the train to reach the crossing even under 
these circumstances a derailing device is used. This derailing 
arrangement is shown in Fig. 14, about 300 feet from the cross- 
ing, although it may be placed from 300 to 500 feet from that 
point. Its purpose is to derail any train attempting to make 
the crossing against the danger signal. The operation of the 
derail is evident from the skeleton lines of the figure. When 
the home signal is at danger the movable part of the derailing 
device is at this point turned so as to catch the flanges of the 
wheels as they attempt to pass it. The train is thus thrown 
upon the cross-ties at such a distance from the crossing as will 
produce a stop before reaching it. When the home signal is at 
safety the derail operated with the signal is closed and the line 
is continuous. This combination of signals and derail coacting 
serves efficiently to prevent collisions at crossings, although trains 
may be occasionally derailed in accomplishing that end. The 
preceding explanations of the use of signals and derail apply to a 
train that may approach the crossing in either direction on either 
track, as is obvious from an inspection of the diagram itself. 



352 



SOME FEATURES OF RAILROAD ENGINEERING. 



283. Signalling at a Double-track Crossing. — In the case of a 
double-track crossing, the arrangement of signals and derails 
is precisely the same as for a single-track crossing, each set of 
signals shown in Fig. 15 covering one track. In other words, 



13JI 
8 




,,-"10 

11 115 nifi 


1 V 






3- XV ^ 
















a. 
,10 



Fig. 15. 

the line of single track is to take the place of each rail with its 
set of signals in that figure. There will be but four derails, one 
for each track only on the approach to the crossing. The working 
of the signals with the derails is precisely the same as has already 
been explained for the single-track crossing. 

284. Signalling for Double-track Junction and Cross-over. — ■ 
Fig. 16 represents a skeleton diagram of signals required for a 
junction of two double-track roads and a cross-over. This 
arrangement covers the use of switches. The location of signals 




Fig. 16. 
and signal cabin as shown is self-explanatory, after what has 
already been stated in connection with single- and double-track 
crossings. It will be observed that the home signals for both 
the west-bound main and branch tracks are identical in loca- 
tion, and are shown by the solid double flag, the distant signal 
being shown by its notched end at a considerable distance back 



GENERAL OBSERVATIONS. 353 

of the double home signal. It will, furthermore, be observed 
that at each home signal there is a derailing-switch interlocked, 
in the lock-and-block system presently to be explained, with the 
home signals operated simultaneously with them. If, therefore, 
an engineman attempts to run his train past a home signal set 
at danger, the result will be the derailment of his train, thus 
brought to rest before it can make any collision with another. 
It is obvious in this case that if the switches from the main to 
the branch tracks or at the extremities of the cross-over are 
worked independently, they must be operated directly in con- 
nection with the signals. For complete protection they should 
be interlocked with the signals so that it would be impossible 
to clear any signal without simultaneously setting the switches 
consistently with those signals. The diagram exhibits clearly 
the indications which must be made in order to effect any 
desired train movement at such a junction of tracks. 

285. General Observations. — Similar arrangements of signals, 
derails, or switches must be made wherever switches, cross-overs, 
and junctions are found, the detailed variations of those signals 
and switches being made to meet the individual requirements 
of each local case. The combinations of switches and switch- 
signals frequently become very complicated in yards where the 
tracks are numerous and the combinations exceedingly varied, in 
order to meet the conditions created by the movement of trains 
into and out of the yard. 

The preceding explanations are intended only to give a clear 
idea of the main features of signalling, in order to secure the high- 
est degree of safety and facility in the movement of trains over 
a modern railroad. While they exhibit the external or apparent 
combinations of signals for that purpose, they do not touch in 
detail and scarcely in general upon the mechanical appliances 
found in the signal cabin and along the tracks required to accom- 
plish the necessary signal movements. The considerations in 
detail of those appliances would cover extended examinations 
of purely mechanical, electrical, pneumatic, and electro-pneu- 
matic combinations too involved to be set forth in any but the 
most extended and careful study. They have at the present 
time been brought to a wonderful degree of mechanical perfection 



354 



SOME FEATURES OF RAILROAD ENGINEERING. 



and afford a field of most interesting and profitable study, into 
which, however, it is not possible in these general statements 
of the subject to enter. 

286. Interlocking-machines. — The earhest machine perfected 
for use in this department of railroad signalling was the Saxby 




Fig. 17. 

and Farmer interlocking-machine, first brought out in England 
and subsequently introduced in this country between 1874 and 
1876. This machine has been much improved since and has 
been widely used. Other interlocking-machines have also been 
devised and used in this country in connection with the most 
improved systems of signalling, until at the present time a high 
degree of mechanical excellence has been reached. 

The interlocking-machine in what is called the lock-and-block 
system of signalling is designed to operate signals, or signals 
in connection with switches, derailing-points, or other dangerous 



INTERLOCKING-MACHINES. 355 

track features, so as to make it impossible for a signalman to make 
a wrong combination, that is, a combination in which the signals 
will induce the engineman to run his train into danger. The 
signals and switches or other track details are so connected and 
interlocked with each other as to form certain desired combina- 
tions by the movement of designated levers in the signal cabin 
or tower. These combinations are predetermined in the design 
and connections of the appliances used, and they cannot be 
changed when once made except by design or by breakage of 
the parts ; they cannot be deranged by any action of the signal- 
man. He may delay trains by awkward or even wrong move- 
ment of levers, but he cannot actually clear his signals for the 
movement of a train without simultaneously giving that train 
a clear and safe track. As has been stated, he cannot organize 
an accident. Figs. 17 and 18 show banks or series of levers 
belonging to interlocking-machines. As is evident from these 
figures, the levers are numerous if the machine operates the 
switches and signals of a large yard, for the simple reason that a 
great many combinations must be made in order to meet the 
requirements of train movements in such a yard. The signal- 
man, however, makes himself acquainted with the various com- 
binations requisite for outgoing and incoming trains and the 
possible movements required for the shifting or hauling out of 
empty trains. He has before him diagrams showing in full the 
lever movements which must be made for the accomplishment 
of any or of all these movements, and he simply follows the direc- 
tions of the diagrams and his instructions in the perfoiTnance 
of his duty. He cannot derange the combinations, although he 
may be slow in reaching them. The locking-frame which com- 
pels him to make a clear track whenever his signals give a clear 
indication to the engineman lies below the lower end of the 
levers seen in the figures. The short arms of the levers carry 
tappets with notches in their edges into which fit pointed pieces 
of metal or dogs ; the arrangement of these notches and dogs is 
such as to make the desired combinations and no others. It will 
be observed that a spring-latch handle projects from a point near 
the upper end of each lever where the latter is grasped in operat- 
ing the machine. This spring-latch handle must be pressed 



356 SOME FEATURES OF RAILROAD ENGINEERING. 




APPLYING POWER IN SYSTEMS OF SIGNALLING. 357 

close to the lever before the latter can be moved. The pressing 
of the spring-latch handle against the lever effects a suitable 
train of unlocking before which the lever cannot be moved and 
after which it is thrown over to the full limit and locked there. 
The desired combination for the movement of the train through 
any number of switches may require a similar movement of a 
number of levers, but the entire movement of that set, as required, 
must be completely effected before the signals are cleared, and 
when they are so cleared the right combination forming a clear 
track for the train, and that one only, is secured. These meagre 
and superficial statements indicate in a general way, however 
imperfectly, the ends attained in a modern interlocking-machine. 
They secure for railroad traffic as nearly as possible an absolutely 
safe track. They eliminate, as far as it is possible to do so, 
the inefficiency of human nature, the erratic, indifferent, or wil- 
fully negligent features of human agency, and substitute there- 
for the certainty of efficient mechanical appliances. In some 
and perhaps many States grade crossings are required by statute 
to adopt measures that are equivalent to the most advanced 
lock-and-block system of signalling. So vast has become railroad 
traffic upon the great trunk lines of the country that it would be 
impossible to operate them at all without the perfected modem 
systems of railroad signalling. They constitute the means by 
which all train movements are controlled, and without such sys- 
tems great modern railroads could not be operated. 

The swiftly moving ' ' limited ' ' express passenger trains, 
equipped with practically every luxury of modem life, speed 
their way so swiftly and smoothly over many hundreds of miles 
without the incident of an interruption, and in such a regular 
and matter-of-fact way, that the suggestion of an intricate system 
of signalling governing its movements is never thought of. Yet 
such a train moves not a yard over its track without the saving 
authority of its block signals. If the engineman were to neglect 
even for a mile the indication of the semaphore, he would place 
in fatal peril the safety of his train and of every life in it. 

287. Methods of Applying Power in Systems of Signalling. — 
The mechanical appliances used in accomplishing these ends are 
among the most efficient in character and delicate yet certain in 



358 SOME FEATURES OF RAILROAD ENGINEERING. 

motive power which engineering science has yet produced. The 
electric circuit formed by the rails of the track plays a most im- 
portant part, particularly in securing the safety of the rear of 
the train in making it absolutely certain whether even rear cars 
that may have broken away have either passed out of the block 
or are still in it. The electric circuit in one application or another 
was among the earliest means used in railroad signalling. Elec- 
tric power is also used in connection with compressed air for the 
working of signals. Among the latest and perhaps the most 
advanced types of lock-ancl-block signalling is that which is 
actuated by low-pressure compressed air, the maximum pressure 
being 15 pounds only per square inch. The compressed air is 
supplied by a simple compressor, and it is communicated from 
the signal cabin to the most remote signal or switch by pipes 
and suitable cylinders fitted with pistons controlled by valves, 
thus effecting the final signal or switch movements. It has been 
successfully applied at the yard of the Grand Central Station in 
New York City and at many other similar points. In this con- 
nection it is interesting to observe that while the original Saxby 
and Farmer interlocking-machine was installed from England in 
this country, as has already been observed, about 1875, American 
engineers have within a year reciprocated the favor by furnishing 
and putting in place most successfully in one of the great railroad 
yards of London the first low-pressure pneumatic lock-and-block 
system * found in Great Britain. 

288. Train-staff Signalling. — The lock-and-block system gives 
the highest degree of security attainable at the present time for 
double-track railroad traffic, but the simpler character of the 
single-track railroad business can be advantageously controlled 
by a somewhat simpler and less expensive system, which is a modi- 
fication of the old train-staff method. It is one of the ' ' machine " 
methods of signalling. The type which has been used widely 
in England, Australia and India, and to some extent in this 
country is called the Webb and Thompson train-staff machine, 
shown in Fig. 19. It will be observed that the machine contains 
ten staffs (18 to 20 inches long and i to i^ inches in diameter), 
but as many as fifteen are sometimes used. These staffs can be 

* By Standard Railroad Signal Company of Troy, N. Y. 



TRAIN-STAFF SIGNALLING. 



359 



removed from the machine at one end of a section of the road 
at which a train is to enter, only by permission from the operator 
at the farther end of the section. If the station at the entrance 
to that section is called A, and the station at the farther end X, 
the following description of the operation of the instrument is 
given by Mr. Charles Hansel in a very concise and excellent man- 
ner: 

' ' When a train is ready to move from A to A' the operator at 
A presses down the lever which is seen at the bottom of the right- 
hand dial, sounding one bell at A', which is for the purpose of 
calling the attention of the operator 
at X to the fact that A desires to 
send a train forward. The operator 
at X acknowledges the call by press- 
ing the lever on his instrument, 
sounding a bell in the tower at A. 
The operator at A then asks per- 
mission from A" to withdraw staff by 
pressing down the lever before men- 
tioned three times, giving three rings 
on the bell at A', and immediately 
turns his right-hand pointer to the 
left, leaving it in the horizontal 
position pointing to the words ' For 
staff,' indicating that he desires 
operator at X to release his instru- 
ment so that he can take a staff or 
train order from it. If there is no 
train or any portion of a train 
between A and A, the holding down 
of the lever at A closes the circuit 
in the lock magnets at A, which 
enables the operator at A to with- 
draw a staff. As soon as this staff is 
removed from A, A turns the left-hand pointer to the words 
'Staff out,' and in removing this staff from the instrument A 
the galvanometer needle which is seen in the centre of the instru- 
ment between the two dials vibrates, indicating to the operator 




Fig. 19.— Webb and Thompson 
Train-staff Machine. 



360 SOME FEATURES OF RAILROAD ENGINEERING. 

at X that A has withdrawn his staff. A' then releases the lever 
which he has held down in order that A might withdraw a staff 
and turns his left-hand indicator to 'Staff out,' and with this 
position of the instrument a staff cannot be withdrawn from 
either one. 

" The first method of delivering this staff to the engineer as a 
train order was to place it in a staff -crane, which crane was located 
on the platform outside of the block station. With the staff in 
this position it has been found in actual practice that the engine- 
man can pick it up while his train is running at a speed of 30 miles 
per hour. A second staff cannot be removed from A nor a staff 
removed from X until this staff which was taken by the engine- 
man in going from A to A' is placed in the staff instrument at X ; 
consequently the delivering of a staff from A to the engineman 
gives him absolute control of the section between A and X. 

' ' This train-order staff also controls all switches leading from 
the main line between A and X, for with the style of switch-stand 
which we have designed for the purpose the trainman cannot 
open the switch until he has secured the staff from the engine- 
man and inserted it in the switch-stand, and as soon as he throws 
the switch-lever and opens the switch he fastens the train-staff 
in the switch-stand, and it cannot be removed until the switchman 
has closed and locked the switch for the main line. When this 
is done he may remove the train-staff and return it to the engine- 
man. It will thus be seen that this train order, in the shape of a 
staff, gives the engineman absolute control over the section, and 
also insures that all switches from the main line are set properly 
before he can deliver the train-staff to the instrument at X. 

' ' In order that the operator at X may be assured that the en- 
tire train has passed his station, we may divide the staff in two 
and deliver one half to the engineman and the other half to the 
trainman on the caboose or rear end of the train, and it will be 
necessary for the operator at X to have the two halves so that 
he may complete the staff in order to insert it into the staff instru- 
men . at X, as it is impossible to insert a portion of the staff ; it 
must be entirely complete before it can be returned to the staff 
instrument." 

Instead of using the entire staff as a whole or in two parts, 



TRAIN-STAFF SIGNALLING. 361 

Mr. Hansel suggests that one or more rings on the body of the 
staff be removed from the latter and given to the engineman or 
other trainman to be placed upon a corresponding staff at the 
extreme end of the section. This would answer the purpose, 
for no staff can be inserted in a machine unless all the rings are 
in their proper positions. These rings can be taken up by a 
train moving at any speed from a suitable crane at any point 
alongside the track. 

For a rapid movement of trains on a single-track railroad 
under this staff system an engineman must know before he 
approaches the end of the section whether the staff is ready for 
delivery to him. In order to accomplish that purpose the usual 
distant and home signals may readily be employed. The distant 
signal would show him what to expect, so that he would approach 
the entrance to the section either at full speed or with his train 
under control according to the indication. Similarly, electric 
circuits may be employed in connection with the staff or rings in 
the control of signals which it may be desired to employ. 

The electric train-staff may also be used in a permissive block 
system, the section of the track between stations A and X con- 
stituting the block. In Fig. 19, showing the machine, a hori- 
zontal arm is seen to extend across its face and to the right. 
This is the permissive attachment which must be operated by the 
special staff shown on the left half of the machine about midway 
of its height. If it is desired to run two or three trains or two 
or three sections of the same train from A before admitting a 
train at A' in the opposite direction, the operator at A so advises 
the operator at A". The latter then permits A to remove the 
special staff with which the extreme right-hand end of the per- 
missive attachment is unlocked and a tablet taken out. This 
tablet is equivalent to a train order and is given to the train 
immediately starting from A. A second tablet is given in a 
similar manner to the second section or train, and a third to the 
third section. The last section of train or train itself starting 
from A takes all the remaining tablets and the special staff for 
insertion in the machine at A". In this manner head-to-head 
collisions are prevented when a number ' of trains are passing 
through the block in the same direction before the entrance of a 



362 



SOME FEATURES OF RAILROAD ENGINEERING. 



train in the opposite direction. This system has been found to 
work satisfactorily where it has been used in this country, al- 
though its use has been quite limited. Evidently, in itself, it is 
not sufficient to prevent rear-end collisions in a block between 
trains moving in the same direction. In order to avoid such 
collisions where a train falls behind its schedule time or for any 
reason is stopped in a block, prompt use must be made of rear 
flagmen or other means to stop or to control the movement of 
the first following train. 




Fig. 20. 

The most improved form of high-speed train-staff machine is 
shown in Fig. 20, as made and installed by the Union Switch 
and Signal Company and used by a number of the largest railroad 
systems of the United States. In these machines the staffs are 
but a few ounces in weight. 



CHAPTER XXIII. 

289. Evolution of the Locomotive. — The evolution of the 
steam locomotive may be called the most spectacular portion 
of the development of railroad engineering. The enormous 
engines used at the present time for hauling both heavy freight 
and fast passenger trains possess little in common, in respect 
of their principal features, with the crude machines, awkward in 
appearance and of little hauling capacity, which were used in the 
early part of the nineteenth century in the beginning of railroad 
operation. The primitive and ill-proportioned machine, ungainly 
in the highest degree, designed and built by Trevithick as far 
back as 1803, was a true progenitor of the modem locomotive, 
although the family resemblance is not at first very evident. 
Several such locomotive machines were designed and operated 
between 1800 and 1829 when Stevenson's Rocket was brought 
out. The water was carried in a boiler on a wagon immediately 
behind the engine, and the steam-cylinder in those early machines 
was placed almost anywhere but where it now seems to belong. 
The Rocket has some general features of resemblance to the 
machines built seventy years later, but when placed side by side 
it might easily be supposed that seven hundred years rather than 
seventy had elapsed between the two productions of the shop. 

After the famous locomotive trial in which Robert Stevenson 
distanced his competitors, the design of the locomotive advanced 
rapidly, and it was but a few years later when the modern loco- 
motive began to be accurately foreshadowed in the machines 
then constructed. This was true both in England and the United 
States. 

The first steam locomotive in this country is believed to be 
the machine built by John Stevens at Hoboken, N. J., in 1825 
and operated in 1825-27. This locomotive has practically the 

363 



364 SOME FEATURES OF RAILROAD ENGINEERING. 

arrangement of boiler and cylinder which is found upon the 
modem contractors' engines used for pile-driving, hoisting, and 
similar operations. It would certainly be difficult to imagine 
that it had any relation to the great express and freight locomo- 
tives of the present day. The rectilinear motions of the piston 
were transformed into the rotary motion of the wheels by means 
of gearing consisting of a simple arrangement of cog-wheels. 
About the same time a model of an English locomotive called 
the Stockton and Darlington No. i was brought to the United 
States by Mr. William Strickland of Philadelphia. The next 
important step in American locomotive development was the 
construction of the locomotive " John Buh" for the Camden and 
Amboy Railroad Company in the English shops of Stevenson & 
Company in the years 1830-31. This machine has the general 
features, although not the large dimensions, of many modem 
locomotives. The cow-catcher is a little more elaborate in 
design and far-reaching in its proportions than the similar ap- 
pendage of the present day, but the general arrangement of the 
fire-box and boiler, the steam-cylinders, the driving-wheels and 
smoke-stack is quite similar to a modern American locomotive. 
This machine, "John Bull," and train made the trip from New 
York City to Chicago and return under its own steam in 1893. It 
was one of the prominent features of the World's Columbian Ex- 
position. It rests in the National Museum at Washington, where 
it is one of the most interesting early remains of mechanical 
engineering in this country. One of the cars used in this train 
was the original used on the Camden and Amboy Road about 
1836. Its body was used as a chicken-coop at South Amboy, N. J., 
for many years, and was rescued from this condition of degrada- 
tion for the purpose of the Exposition trip in 1893. The original 
driving-wheels had locust spokes and felloes, the hubs and tires 
being of iron. 

The locomotive "George Washington" was built, as a con- 
siderable number have been since, with one driving-axle, and was 
designed to be used on heavy grades. This machine was built by 
William Norris & Sons of Philadelphia, who were the progenitors 
of the present great establishment of the Baldwin Locomotive 
Works. While the development of the locomotive was sub- 



INCREASE OF LOCOMOTIVE WEIGHT. 365 

jected to many vicissitudes in principles, general arrangement, 
and size in order to meet the varying requirements of different 
roads as well as the fancies or more rational ideas of the designers, 
its advance was rapid. As early as 1846 we find practically the 
modern consolidation type, followed in 1851 by the ordinary 
eight-wheel engine of which thousands have been constructed 
within the pa t fifty years. The first Mogul built by the Baldwin 
Locomotive Works was almost if not quite as early in the field. 
Both these types of machines carry the principal portion of their 
weight upon the driving-wheels and were calculated to yield a 
high tractive capacity, especially as the weights of the engines 
increased. The weight of the little ' 'John Bull" was but 22,425 
pounds, while that of the great modern machine may be as much 
as 267,800 pounds, with 53,500 pounds on a single driving-axle. 

290. Increase of Locomotive Weight and Rate of Combustion 
of Fuel. — The development of railroad business in the United 
States has been so rapid as to create rigorous exactions of every 
feature of a locomotive calculated to increase its tractive force. 
Any enhancement of train-load without increasing the costs of 
the train force or other cost - of movement will obviously lead 
to economy in transportation. In order that the locomotive 
may yield the correspondingly augmented tractive force the 
weight resting upon the drivers must be increased, which means 
a greater machine and at the same time higher working pressures 
of steam. This demands grea er boiler capacity and strength 
and a proportionately increased rate of combustion, so as to 
move the locomotive and train by the stored-up energy of the 
fuel transformed in the engine through steam pressure The 
higher that pressure the gr ater the amount of energy stored 
up in a unit of weight of the steam and the greater will be the 
capacity of a given amount of water to perform the work of 
hauling a train. The greater the weight of train moved and 
the greater its speed the more energy must be supplied by the 
steam, and, again, that can only be done with a correspondingly 
greater consumption of fuel. In the early days of the small and 
crude machines to which allusion has already been made the 
simplest fuel was sufficiently effective. As the duties performed 
by the locomotive became more intense a higher grade of fuel. 



366 SOME FEATURES OF RAILROAD ENGINEERING. 

i.e., one in which a greater amount of heat energy is stored per 
unit of weight, was required. Both anthracite and bituminous 
coal have admirably filled these requirements. The movement 
of a great modern locomotive and its train at an average rate 
of 30 to 60 miles per hour requires the combustion of fuel at a 
high rate and the rapid evapo.ation of steam at pressures of 
180 to 225 or more pounds per square inch. The consumption 
of coal by such a locomotive may reach 100 pounds per minute, 
and two barrels of water may be evaporated in the same time. 
This latter rate would require over a gallon of water per second 
to be ejected through the stack as exhaust steam. Some of the 
most marked improvements in locomotive practice have been 
made practically within the past six or seven years in order to 
meet these exacting requirements. 

While the operations of locomotives will obviously depend 
largely upon quality of fuel, speed, and other conditions, the 
investigations of Prof. W. F. M. Goss and others appear to indi- 
cate that 12 to 14 poimds of water per hour may be evaporated 
by a good locomotive boiler per square foot of heating surface, 
and that 25 to 30 pounds of steam will be required per indicated 
horse-power per hour, 

291. Principal Parts of a Modem Locomotive.^ — The principal 
features of a modern locomotive are the boiler with the smoke- 
stack placed on the front end and the fire-box or furnace at the 
rear, the tubes, about 2 inches in diameter, through which the 
hot gases of combustion pass from the furnace to the smoke- 
stack, the steam-cylinders with their fittings of valves and valve 
movements, and the driving-wheels. These features must all 
be designed more or less in reference to each other, and whatever 
improvements have been made are indicated almost entirely 
by the relative or absolute dimensions of those main fea- 
tures. The boiler must be of sufficient size so that the water 
contained in it may afford a free steam production, requiring 
in turn a corresponding furnace capacity with the resulting 
heating surface. The latter is that aggregate surface of the 
interior chambers of the boiler through which the heat pro- 
duced by combustion finds its way to the water evaporated in 
steam; it is composed almost entirely of the surfaces of the 



THE WOOTTEN FIRE-BOX AND BOILER. 



367 



steel plates of the fire-box and of the numerous tubes running 
through the boiler and parallel to its centre, exposed to the hot 
gases of combustion and in contact with the water on the op- 
posite sides of those plates. Evidently an increase in size of the 
fire-box with the correspondingly increased combustion will 
furnish a proportionally larger amount of steam at the desired 
high pressure, but an increase in the size of the fire-box is limited 
both in length and in width. It is found that it is essentially 
impracticable for a fireman to serve a fire-box more than about 
lo feet in length. The maximum width of the locomotive limits 
the width of the fire-box. 

292. The Wootten Fire-box and Boiler. — ^As the demand arose 
for an enlarged furnace the width of the latter was restricted by 
the width between the driving-wheel tires, less than 4 feet 6 inches. 
That difficulty was overcome by what is known as the Wootten 
fire-box, which was brought out by John E. Wootten of the Phila- 




Fig. 21. 

delphia and Reading Railroad about 1877, and has since been 
developed and greatly improved by others. The Wootten 
boiler with its sloping top and great width extending out over 
the rear driving-wheels presented a rather curious appearance 
and was a distinct departure in locomotive-boiler design. Fig. 
21 shows an elevation and two sections of the original Wootten 



368 SOME FEATURES OF RAILROAD ENGINEERING. 

type of boiler. It will be noticed that in front of the fire-box 
there is a combustion-chamber of considerable length, 2^ to 3 feet 
long. This boiler was first designed to bum the poorer grades 
of fuel, such as coal-slack, in which the combustion-chamber to 
complete the combustion of the fuel was thought essential. By 
Wootten's device, i.e., extending the boiler out over the driving- 
wheels, a much greater width of fire-box was secured, but the 
height of the locomotive was considerably increased. It cannot 
be definitely stated just how high the centre of the locomotive 
boiler may be placed above the track without prejudice to safety 
in running at high speeds, but it has not generally been thought 
best to lift that centre more than about 9^ feet above the tops 
of rails, and this matter has been held clearly in view in the 
develoxjment of \h2 wide fire-box type of locomotive boilers. 

Like every other new form of machine, the Wootten boiler 
developed some weak features, although there was no disappoint- 
ment in its steaming capacity. It will be noticed in the figure 
that the plates forming that part of the boiler over the fire-box 
show abrupt changes in curvature which induced ruptures of 
the stay-bolts and resulted in other weaknesses. This boiler 
passed through various stages of development, till at the present 
time Figs. 22 and 23 show its most advanced form, which is 
satisfactory in almost or quite every detail. The sudden changes 
in direction of the plates in the first Wootten example have been 
displaced by more gradual and easy shapes. Indeed there are 
few features other than those which characterize simple and easy 
boiler construction. The enormous grate area is evident from 
the horizontal dimensions of the fire-box, which are about 120 
inches in length by about 106 inches in breadth. The boiler 
has over 4000 square feet of heating surface and carries about 
200 pounds per square inch pressure of steam. The combustion- 
chamber in front of the fire-box has been reduced to a length of 
about 6 inches, just enough for the protection of the expanded 
ends of the tubes. The barrel of the boiler in front of the fire- 
box has a diameter of 80 inches and a length of about 15 feet. 
The grate area is not far from 100 square feet. The improve- 
ments which have culminated in the production of this boiler 
are due largely to Mr. Samuel Higgins of the Lehigh Valley Road. 



THE WOOTTEN FIRE-BOX AND BOILER. 



369 



511 Tabes 5' DIa. 

480 Screw Sl»jsl!^"Dl». 
1255 " " r 



-. ,_. .^ Plan of Domo Ring 
24 Smd« ^-~~ ^' I ' 

C»rilNo.llli; 

T2R^.«*tv''Dl'''^'''''''\7'\---4-^ \2« Taper Tap 12 Thd.. 

J Rlveta 1 X Dla. 8«iid Boi Slucl»';^f .„ ! ,' ' -1 ^-aj^'Taper Tap 12 Thds. 



Vlmaof 
Steam DomeJU&er 




2}j Taper Tap 12 Thds. 
Taper Ji "in IS ° 



Fig. 22. 



Plan of Longitudinal Seam 

JVew Vorh Railroad Cluh 




2J<" Taper Tap 12 Thdj 
Taper ^4" in 12* 



Fig. 23. 



370 SOME FEATURES OF RAILROAD ENGINEERING. 

293. Locomotives with Wootten Boilers. — Fig. 24 exhibits a 
consolidation freight locomotive of the Lehigh Valley Railroad, 
having the boiler shown in Figs. 22 and 23. This machine is 
one of the most efficient and powerful locomotives produced 
at the present time. The locomotive shown in Fig. 25 has a 
record. It is one used on the fast Reading express service be- 
tween Philadelphia and Atlantic City during the season of the 
latter resort. It has run one of the fastest schedule trains in 
the world and has attracted attention in this country and abroad. 
Its type is called the Atlantic and, as the view shows, it is 
fitted with the Wootten improved type of boiler. It will be 
noticed that the wide fire-box does not reach out over the rear 




Fig. 24. 

drivers, but over the small trailing-wheels immediately behind 
them. This is a feature of wide locomotive fire-box practice 
at the present time to which recourse is frequently had. There 
is no special significance attached to the presence of the small 
trailing-wheels except as a support for the rear end of the boiler, 
their diameters being small enough to allow the extension of the 
fire-box over them without unduly elevating the centre of the 
boiler. 

The cylinders of these and many other locomotives are known 
as the Vauclain compound. In other' words, it is a compound 
locomotive, there being two cylinders, one immediately over the 
other, on each side. The diameter of the upper cylinder is much 
less than that of the lower. The steam is first admitted into the 
small upper cylinder and after doing its work there passes into 



LOCOMOTIVES WITH WOOTTEN BOILERS. 



371 



the lower or larger cylinder, where it does its work a second time 
with greater expansion. By means of this compound or double- 
cylinder use of the steam a higher rate of expansion is secured and 
a more uniform pull is exerted upon the train, the first generally 
contributing to a more economical employment of the steam, 
which in turn means a less amount of fuel burned for a given 
amount of tractive work performed. 

In the early part of November, 1901, an engine of this type 
hauling a train composed of five cars and weighing 235 tons made 
a run of 55.5 miles between Philadelphia and Atlantic City at 




Fig. 25. 



the rate of 71.6 miles per hour, the fastest single mile being made 
at a rate of a little less than 86 miles per hour. 

The power being developed by these engines runs as high as 
1400 H.P. at high speeds and 2000 H.P. at the lower speeds of 
freight trains. 

The chief economic advantage of these wide fire-box machines 
lies in the fact that very indifferent grades of fuel may be con- 
sumed. Indeed there are cases where fuel so poor as to be 
unmarketable has been used most satisfactorily. With a narrow 
and small fire-box a desired high rate of combustion sometimes 
demands a draft strong enough to raise the fuel over the grate- 
bars. This difficulty is avoided in the large fire-box, where suffi- 
cient combustion for rapid steaming is produced with less inten- 
sity of blast. 



372 



SOME FEATURES OF RAILROAD ENGINEERING. 



294. Recent Improvements in Locomotive Design. — Concur- 
rently with the development of the Wootten type of boiler, other 
wide fire-box types have been brought to a high state of excel- 
lence. In reality general locomotive progress within the past 
few years has been summed up by Mr. F. J. Cole as follows : 

(a) The general introduction of the wide fire-box for burning 
bituminous coal. 

(6) The use of flues of largely increased length. 

(c) The improvements in the design of piston-valves and 
their introduction into general use. 

(d) The recent progress made in the use of tandem compound 
cylinders. 

The piston-valve, to which reference is made, is a valve in 
the shape of two pistons connected by an enlarged stem or pipe 
he entire length of the double piston, the arrangement depend- 
ing upon the length of steam-cylinder or stroke; it may be 31 
or 32 inches. This piston-valve is placed between the steam- 




'^t^'^j^i^'^^'^'*^"^^'^^'^"'^''^^'"'^'^""^"'^'"''^^^ 



Fig. 26. 

cylinder and the boiler, and is so moved by eccentrics attached 
to the driving-wheel axles through the medium of rocking levers 
and valve-stems as to admit steam to the cylinder at the beginning 
of the stroke and allow it to escape after the stroke is completed. 
Fig. 26 shows a section through the centre of one of these piston- 
valves. It will be noticed that the live steam is admitted around 



COMPOUND LOCOMOTIVES WITH TANDEM CYLINDERS. 373 



a central portion of the valve, and that the steam escapes through 
the exhaust-passages at each end of the piston- valve. This type 
of valve is advantageous with high steam pressures for the reason 
that its ' ' blast," i.e., the steam pressure, does not press it against 
its bearings as is the case with the old type of slide-valve, the 
wear of which with modern high steam pressures would be ex- 
cessive, although under more recent slide-valve design this objec- 
tion does not hold. 

295. Compound Locomotives with Tandem Cylinders. — The 
tandem compound locomotive, as recently built, is a locomotive 
in which the high-pressure cylinder is placed immediately in 




Fig. 27. 

front of the low-pressure cylinder and in line with it. In the 
Vauclain type it is necessary to have a piston-rod for each of the 
two cylinders, one above the other, each taking hold of the same 



374 



SOME FEATURES OF RAILROAD ENGINEERING 



X 1 j 



T 



It 



t 



I I I a-0 Vrli 



1.1 



.J^ !i; i:: 







. -a 1-19—4- - 1 — I 1 

I i 




EVAPORATIVE EFFICIENCY AND RATES OF COMBUSTION. 375 

cross-head. In the tandem arrangement with the two cyhnders 
each in line, but one piston-rod is required. An example of a 
locomotive with this tandem arrangement of compound cylinders 
will be shown farther on. 

Figs. -27 and 28 show two sections, one transverse and one 
longitudinal, of a type of large fire-box boiler built by the Ameri- 
can Locomotive Works at Schenectady. The diameter of the 
barrel of the boiler in front of the fire-box is about 5 feet 8 inches, 
while the clear greatest width of the fire-box is 5 feet 4^ inches. 
The length of the latter is 8 feet 7 inches, making a total grate 
area in this particular instance of over 45 square feet. There 
are 338 2 -inch tubes, each 16 feet in length. The total length 
over all of the boiler is 3 1 feet ^ inch. The result of such a design 
is an arrangement by which a large grate area is secured and a 
corresponding high rate of combustion without a too violent 
draft. In designing locomotive boilers for bituminous coal one 
square foot of grate area is sometimes provided for each 60 to 70 
square feet of heating surface in the tubes. 

296. Evaporative Efficiency of Different Rates of Combustion. 
— In the development of this particular class of locomotive 




Fig. 29. 

boilers it is to be remembered that as a rule the highest rates of 
combustion frequently mean a decreased evaporation of water 
at boiler pressure per pound of fuel. Modem locomotives may 
burn over 200 pounds of coal per square foot of grate area per 
hour, and in doing so the evaporation may be less than 5 pounds 



376 SOME FEATURES OF RAILROAD ENGINEERING. 

of water per pound of fuel. On the other hand, when the coal 
burned does not exceed 50 pounds per square foot of grate area 
per hour, as much as 8 poiuids of water may be evaporated for 
each pound of coal. It is judicious, therefore, to have large 
grate area, other things being equal, in order that the highest 
attainable efficiency in evaporation may be reached. 

296a. Tractive Force of a Locomotive. — The tractive force 
of a locomotive arises from the fact that one solid body cannot 
be moved over another, however smooth the surface of contact 
may be, without developing the force called resistance of friction. 
This resistance is measured by what is called the coefficient of 
friction, determined only by experiment. The resistance of 
friction and this coefficient will depend both upon the degree 
of smoothness of the surface of contact and on its character. If 
surfaces are lubricated, as in the moving parts of machinery, 
the force of friction is very much decreased, but in the absence 
of that lubricant it will have a much higher value. The coeffi- 
cient of friction is a ratio which denotes the part of the weight of 
the body moved which must be applied as a force to that body in 
order to put it in motion against the resistance of friction. In 
the case of lubricated surfaces this ratio may be as small as a few 
hundredths. In the case of lo omotive driving-wheels and the 
track on which they rest this value is usually taken at .2 to .25. 

There are times when it is desirable to increase the resistance 
of friction between locomotive drivers and the rails. For this 
purpose a simple device, called the sand-box, is frequently placed 
on the top of a locomotive boiler with pipes running down from 
it so as to discharge the sand on the rails immediately in front 
of the drivers. The sand is crushed under the wheels and offers 
an increased resistance to their slipping. 

The tractive force of a locomotive may also be computed 
from the pressure of steam against the pistons in the steam- 
cylinders. If the indicated horse-power in the cylinder be repre- 
sented by H.P., and if all frictional or other resistance between 
the cylinder and the draw-bar be neglected, the following equality 
will hold : 

Draw-bar pull X speed of train in miles ) tt t> v/ v/ a 

10 \ =H. P. X33, 000X00. 

per hour X 5280 ) 



TRACTIVE FORCE OF A LOCOMOTIVE. 377 

If 5 = speed in miles per hour, and ii T = draw-bar pull, then 
the preceding equality gives 

375XH.P. 



T 



S 



This value of the ' ' pull ' ' must be diminished by the friction of 
the locomotive as a machine, by the rolling resistance of the 
trucks and tender, and by the atmospheric resistance of the 
locomotive as the head of the train. Prof. Goss proposes the 
following approximate values for these resistances in a paper 
read before the New England Railroad Club in December, 1901. 
A number of tests have shown that a steam pressure of 3.8 
pounds per square inch on the piston is required to overcome 
the machine friction of the locomotive. Hence if d is the diam- 
eter of the piston in inches, L the piston-stroke in feet, and D 
the diameter of driver in feet, while / is that part of the draw-bar 
pull required to overcome machine friction, the following equation 
will hold : 

f.7:D=3.S—X2LX2. /. / = 3.8-^. 

Again, if W be the rolling load in tons on tender and trucks 
(exluding that on drivers), and if r be that part of the draw-bar 
pull required to overcome the rolling resistance due to W, then 
experience indicates that approximately, in pounds. 

As before, 5 is the speed in miles per hour. 

Finally, if h be that part of the draw-bar pull in pounds 
required to overcome the head resistance (atmospheric) of the 
locomotive, there may be written approximately 

h = .iiS\ 
The actual draw-bar pull in pounds available for moving the 
train will then be 

The maximum value of t should be taken as one fourth the great- 
est weight on drivers. 



378 SOME FEATURES OF RAILROAD ENGINEERING. 

If H is the total heating surface in square feet, and if 12 
pounds of water be evaporated per square foot per hour, while 
2 8 pounds of steam are required per horse-power per hour, then 

^^^ 12H ^ 375H.P. 161H 

H.P. =^ and '^-'^ = — e"- 

28 o ^ 

Hence 

161H d'L ,^ / 5\ 



5 ^- I? \ 6, 

The actual draw-bar pull in pounds may then be computed by 
this formula. 

Some recent tests of actual trains (both heavy and light) 
on the N. Y. C. & H. R. R. R. between Mott Haven Junction 
and the Grand Central Station, New York City, a distance of 
5.3 miles, by M . Bion J. Arnold, by means of a dynamometer- 
car, gave the actual average draw-bar pull per ton of 2000 pounds 
as ranging from 12 to 25 pounds going in one direction and 
1 2. 1 to 24 pounds in the opposite direction. There were eight 
tests in each direction, and the greatest speed did not exceed 30 
miles per hour. 

As the diameter of the driver appears in the preceding formu- 
la, it may be well to state that an approximate rule for that 
diameter is to make it as many inches as the desired maximum 
speed in miles per hour, i.e., 70 inches for 70 miles, or 80 inches 
for 80 miles, per hour. 

297. Central Atlantic Type of Locomotive. — Fig. 29 represents 
what is termed the Central Atlantic type (single cylinder) of 
engine, which is used for hauling most of the fast passenger 
trains on the New York Central and Hudson River Railroad. 
The characteristics of boiler and fire-box are such as are shown 
in Figs. 27 and 28. 

The cylinders are 21 inches internal diameter, and the stroke 
is 26 inches. The total grate area is 50 square feet, and the total 
heating surface 3500 square feet. The total weight of the loco- 
motive is 176,000 pounds, with 95,000 on the drivers. It will be 
observed that the total weight of locomotive per square foot of 
heating surface is scarcely more than 650 pounds, which is a low 
value. The boiler pressure carried may be 200 pounds per 



CONSOLIDATION ENGINE, N. Y. C. & H. R. R. R. 379 

square inch or more. The tractive force of this locomotive may 
be taken at 24,700 pounds. There is suppHed to these engines, 
among others, what is called a traction-increasing device. This 
traction-increaser is nothing more nor less than a compressed-air 
cylinder secured to the boiler, so that as its piston is pressed out- 
ward, i.e., downward, it carries with it a lever, the fulcrum of 
which is on the equalizing-lever of the locomotive frame, the 
other or short end of the lever being attached to the main bar 
of the frame itself. This operation redistributes the boiler-load 
on the frame, so as to increase that portion which is carried by 
the drivers. This has been found to be a convenient device 
in starting trains and on up grades. In the present instance 
the traction-increaser may be operated so as to increase the load 
on the drivers by about 12,000 pounds. It is not supposed to 
be used except when needed under the circumstances indicated. 




Fig. 30. 

A number of indicator-cards taken from the steam-cylinders 
of these engines hauling the Empire State Express and other 
fast passenger trains on the Hudson River Division of the N. Y. C. 
& H. R. R. R., show that with a train weighing about 208 tons 
while running at a speed of 75 miles per hour 1323 H.P. was 
developed. Fig. 30 shows these indicator diagrams. With a 
train weighing 685 tons 1452 H.P. was indicated at a speed of 
63 miles per hour. 

298. Consolidation Engine, N. Y. C. & H. R. R. R. — One of 
the heaviest wide fire-box compound consolidation engines re- 
cently built for the New York Central freight service is shown 
in Fig. 31. It will be noticed that there is but one cylinder on 
each side of the locomotive, and that they are of different diam- 



380 



SOME FEATURES OF RAILROAD ENGINEERING. 



eters. One of these cylinders, 23 inches inside diameter, is a 
high-pressure cylinder, and the other, 3 5 inches inside diameter, is 
a low-pressure cylinder, the stroke in each case being 34 inches. 
The total grate area is 50.3 square feet, the fire-box being 8 feet 
long by 6 feet 3 inches wide. The total heating surface is 3480 
square feet. The diameter of the barrel of the boiler at the front 
end is 72 inches, and the diameter of the drivers 63 inches. The 




Fig. 31. 

pressure of steam in the boiler is 210 pounds per square inch. 
The total weight of the locomotive is 194,000 pounds, of which 
167,000 rests upon the drivers. These engines afford a maxi- 
mum tractive force of 37,900 pounds. This engine is typical of 
those used for the New York Central freight service. They have 
hauled trains weighing nearly 2200 tons over the New York 
Central road. 

299. P., B. & L. E. Consolidation. — The consolidation loco- 
motive shown in Fig. 32 is a remarkable one in that it was for 
a time the heaviest constructed, but its weight has since been 
exceeded by at least two of the Decapod type built for the Sante 
Fe company. It was built at the Pittsburg works of the Ameri- 
can Locomotive Company for the Pittsburg, Bessemer and Lake 
Erie Railroad to haul heavy trains of iron ore. The total weight 
is 250,300 pounds, of which the remarkable proportion of 225,200 
is carried by the drivers. The tender carries 7500 gallons of 



L. S. cfc M. S. FAST PASSENGER ENGINE. 



381 



water, and the weight of it when loaded is 141,100 pounds, so 
that the total weight of engine and tender is 391,400 pounds. 
The average weight of engine and tender therefore approaches 
7000 pounds per lineal foot. This is not a compound locomotive, 




Fig. 32. 

but each cylinder has 24 inches inside diameter and 32 inches 
stroke, the diameter of the driving-wheels being 54 inches. The 
boiler carries a pressure of 220 pounds, and the tractive force of 
the locomotive is 63,000 pounds. 

A noticeable feature of this design, and one which does not 
agree with modern views prompting the design of wide fire-boxes, 
is its great length of 1 1 feet and its small width of 3 feet 4^ inches. 
There are in the boiler 406 2^-inch tubes, each 15 feet long, the 
total heating surface being 3805 square feet. 

300. L. S. & M. S. Fast Passenger Engine. — The locomotive 
shown in Fig. 33 is also a remarkable one in some of its features, 
chief among which is the 19 feet length of tubes. It was built at 
the Brooks works of the American Locomotive Company for the 
Lake Shore and Michigan Southern Railroad. The total weight 
of engine is 174,500 pounds, of which 130,000 pounds rests upon 
the drivers. The rear truck carries 23,000 pounds and the front 



383 



SOME FEATURES OF RAILROAD ENGINEERING. 



truck 21,500 pounds. This is not a compound engine. The 
cyhnders have each an inside diameter of 20^ inches, and 28 inches 
stroke. As this locomotive is for fast passenger traffic, the driv- 
ing-wheels are each 80 inches in diameter, and the driving-wheel 




Fig. 33. 

base is 14 feet. The fire-box is 85X84 inches, giving a grate 
area of 48^ square feet and a total heating surface of 3343 square 
feet. There are 285 2|-inch flues, each 19 feet long. The tender 
carries 6000 gallons of water. Cast and compressed steel were 
used in this design to the greatest possible extent, and the result 
is shown in that the weight divided by the square feet of heating 
surface is 52.18 pounds. 

301. Northern Pacific Tandem Compound Locomotive. — The 
diagram shown in Fig. 34 exhibits the outlines and main features 
of a tandem compound locomotive to which allusion has already 
been made. It was built at Schenectady, New York, in 1900, 
for the Northern Pacific Railroad, and was intended for heavy 
service on the mining portions of that line. 

The diameters of the high- and low-pressure cylinders are 
respectively each 15 and 28 inches, with a stroke of 34 inches, 
while the boiler pressure is 225 pounds per square inch. The 
total weight of the machine is 195,000 pounds and the weight 
on the drivers 170,000 pounds, the diameter of the drivers being 
55 inches. As the figure shows, it belongs to the consolidation 
type. The fire-box is 10 feet long by 3.5 feet wide, giving a 



NORTHERN PACIFIC TANDEM COMPOUND LOCOMOTIVE. 383 




384 



SOME FEATURES OF RAILROAD ENGINEERING. 



grate area of 35 square feet, with which is found a total heating 
surface of 3080 square feet. There are 388 2-inch tubes, each 14 
feet 2 inches long. These engines are among the earliest com- 
pound-tandem type and have been very successful. Other 
locomotives of practically the same general type have been 
fitted with a wide fire-box, 8 feet 4 inches long by 6 feet 3 inches 
wide, with the grate area thus increased to 52.3 square feet. 

302. Union Pacific Vauclain Compound Locomotive. — The 
next example of modern locomotive is the Vauclain compound 
type used on the Union Pacific Railroad. It is a ten-wheel pas- 




FiG. 35. 

senger engine and one of a large number in use. The weight 
on the drivers is 142,000 pounds, and the total weight of the 
locomotive is about 185,000 pounds. The high-pressure cylinder 
has an inside diameter of 15^ inches, while the low-pressure cylin- 
der has a diameter of 26 inches. The stroke is 28 inches and 
the diameter of the driving-wheels 79 inches. On the Union 
Pacific Railroad the diameter of the driving-wheel varies some- 
what with the grades of the divisions on which the engines run. 

In some portions of the country, as in Southern California, 
oil has come into quite extended use for locomotive fuel. 

303. Southern Pacific Mogul with Vanderbilt Boiler. — The 
locomotive shown in Fig. 36 belongs to the Mogul type, having 
three pairs of driving-wheels and one pair of pilots. It is fitted 
with the Vanderbilt boiler adapted to the use of oil fuel. The 



THE "COO" DECAPOD LOCOMOTIVE. 



385 



locomotives of which this is an example were built for the South- 
ern Pacific Company, and they have performed their work in a 
highly satisfactory manner. They are not particularly large 
locomotives as those matters go at the present day, as they carry 




Fig. 36. 

about 135,000 pounds on the drivers and 22,000 pounds on the 
truck, giving a total weight of 157,000 pounds. The character- 
istic feature of the machine is its adaptation to the burning of 
oil, which requires practically no labor in firing, although the 
services of a fireman must still be retained. 

304. The " Soo " Decapod Locomotive. — It has been seen that 
the results of Trevethick's early efforts was a crude and simple 
machine, with what might be termed, in courtesy to that early 
attempt, a single pair of drivers. Subsequently, as locomotive 
evolution took place, two pairs of drivers coupled with the 
horizontal connecting-rod were employed. Then the Mogul 
with the three pairs of coupled drivers was used, and at or 
about the same time the consolidation type with four pairs 
of coupled drivers was found adapted in a high degree to the 
hauling of great freight trains. The last evolution in driving- 
wheel arrangement is exhibited in Fig. 37. It belongs to what is 
called the Decapod type. As a matter of fact, five pairs of 
coupled driving-wheels have been occasionally used for a con- 
siderable number of years, but this engine is the Decapod brought 
up to the highest point of modern excellence. As shown, it uses 
steam by the Vauclain compound system, the small or high- 
pressure cylinder being underneath the low-pressure cylinder. 
They have been built by the Baldwin Locomotive Works for 



386 



SOME FEATURES OF RAILROAD ENGINEERING. 



the Minneapolis, St. Paul and Sault Ste. Marie Railroad Com- 
pany, on what is called the "Soo Line." It has given so much 
satisfaction that more of this type but of greater weight are 
being built for the same company. This engine was limited to 




Pre. 37- 

a total weight of 215,000 pounds, with 190,000 pounds on the 
drivers. 

305. The A,, T, & S. F. Decapod, the Heaviest Locomotive yet 
Built. — The heaviest locomotive yet constructed, consequently 
occupying the primacy in weight, is that shown in Fig. 38. It 
is a Decapod operated with others of its type by the A., T. & S. F. 




Fig. 38. 



Company near Bakersfield, California. It is a tandem compound 
coal-burner, as shown by the illustration, the high-pressure cylin- 
der being in front of the low-pressure. The dimensions of cylin- 
ders are 19 and 32 X 32 inches stroke, and the driving-wheels are 
57 inches in diameter. The total height from the top of stack 



THE HEAVIEST LOCOMOTIVE YET BUILT. 



387 








— /^^J- 



388 



SOME FEATURES OF RAILROAD ENGINEERING. 



down to the rail is 1 5 feet 6 inches, while the height of the centre 
of the boiler above the rails is 9 feet 10 inches. Figs. 39 and 40 
show some of the main boiler and fire-box dimensions. There 
are 463 2|-inch tubes, each 19 feet long. The total heating sur- 
face is 5390 square feet, about one eighth of an acre, the length 
of the fire-box being 108 inches and the width 78 inches. The 
heating surface in the tubes is 5 1 56 square feet, and in the fire-box 
210.3 square feet; the grate surface having an area of 58.5 square 
feet. The boiler is designed to carry a working pressure of 225. 




pounds per square inch, the boiler-plates being If inch, 3"^ inch, 
and I inch thick, according to location. As shown by the illus- 
trations, the boiler is what is termed an extended wagon-top 
with wide fire-box. The total weight of the locomotive itself is 
267,800 pounds, while the weight on the driving-wheels is 237,800 
pounds, making 47,560 pounds on each axle. The tractive force 
of this locomotive is estimated to be over 62,000 pounds. 



COMPAIilSOX OF SOME OF THE HEAVIEST LOCOMOTIVES. 389 

306. Comparison of Some of the Heaviest Locomotives in Use. 

— The following table gives a comparison of the heaviest locomo- 
tives thus far built, as taken from the Railroad Gazette for Janu- 
ary 31, 1902, revised to September i, 1902. 

COMPARISON OF HEAVIEST LOCOMOTIVES. 



Name of builder 

Size of cylinders 

Total weight .^ 

Weight on drivers . . . 
Driving-wheels, diam. 

Heating surface 

Grate area 



Atchison, Topeka 
& Santa Fe. 



Baldwin 
19 & 32X32 in. 
267,800 lbs. 
237,8oolbs. 

5 7 in. 
5,390 sq. ft. 
58. 5 sq. ft. 



Pittsburg, 
Bessemer & 
Lake Erie. 



Pittsburg 
24X32 in. 
250,300 lbs. 
225,200 lbs. 

54 in. 
3,805 sq. ft. 
36. S sq. ft. 



Union 
Railroad. 



Pittsburg 
23X32 in. 
230,000 lbs. 
208,000 lbs. 

54 in. 
3,322 sq. ft. 
33.5 sq. ft. 



Illinois 
Central. 



Brooks 
23 X 30 in. 
232,200 lbs. 
193,200 lbs. 

5 7 in. 
3,500 sq. ft. 
37.5 sq. ft. 



Lehigh 
Valley. 



Baldwin 
18 & 30X30 in. 
225,082 lbs. 
202,232 lbs. 

55 in. 
4,104 sq. ft. 
90 sq. ft. 



These instances of modern locomotive construction are im- 
pressive, especially when considered in contrast with the type 
of engine in use not more than fifty years ago. They indicate 
an almost incredible advance in railroad transportation, and they 
account for the fact that a bushel of wheat can be brought over- 
land at the present time from Chicago to New York City, a dis- 
tance of 900 miles, for about one third of the lowest charge for 
delivering a valise from the Grand Central Station in the city 
of New York to a residence within a mile of it. 



PART V. 

THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



307. Feasibility of Nicaragua Route. — The feasibility of a 
ship-canal between the two oceans across Nicaragua has been 
recognized almost since the discovery of Lake Nicaragua in 1522 
by Gil Gonzales de Avila, who was sent out from Spain to succeed 
Balboa, after the execution of the latter by Pedro Arias de Avila 
at Ada on the Isthmus of Panama. 

308. Discovery of Lake Nicaragua. — Gil Gonzales set sail 
from the Bay of Panama in January of that year northward along 
the Pacific coast as far as the Gulf of Fonseca. He landed there 
and proceeded to explore the country with one hundred men, 
and found what he considered a great inland sea, as we now 
know, about 14 miles from the Pacific Ocean at the place of 
least separation. The country was inhabited, and he found a 
native chief called Nicarao, who was settled with his people at 
or near the site of the present city of Rivas. As he found it a 
goodly country, fertile and abounding in precious metals, he 
immediately proceeded to take possession of it for his sovereign, 
but the Spanish explorer was sufficiently gracious to the friendly 
chief to name Lake Nicaragua after him. From that time the 
part of Nicaragua in the vicinity of the lake received much atten- 
tion, and the Spaniards made conquest of it without delay. 
Among those who were the earliest visitors was a Captain Diego 
Machuca, who, with two hundred men under his command, ex- 
plored Lake Nicaragua in 1529 and constructed boats on it, a 
brigantine among them. He seems to have been the first one 
who entered and sailed down the Desaguadero River, now called 

390 



EARLY MARITIME COMMERCE WITH LAKE NICARAGUA. 391 



the San Juan, and one of the rapids in the upper portion of the 
river now bears his name. He pursued his course into the 
Caribbean Sea and sailed eastward to the Isthmus of Panama. 




■8 — 1. Teliuantcpec Route 

2. Fonseca 

3. Realejo 

4. Tamarindo 

5. Brito 
0. S.Juan del Sur 

7. Salinas Baj 

8. Panama Route 
S. San Bias Route 

10. Caledonia Bay Routes 
r 11. Tupiaa-Tiati-Acanti Route 
~1L'. Arsuia-Paya-Tuyra Route 

13. Atrato-Carcarica-Tuyra Route 

14. Atrato-Peranchita-Tuyra Route 

15. Atrato-Truando Route 

16. Atrato-Napipi Route 

17. Atrato-Bojaya Route 
IS. Atrato-Baudo Route 
10. Atrato-Sau Juan Route 



Map of American Isthmus, showing Proposed Canal Routes. 

309. Early Maritime Commerce with Lake Nicaragua. — Sub- 
sequently sea-going vessels passed through the San Juan River 
in both directions and maintained a maritime trade of some mag- 
nitude between the shores of Lake Nicaragua and Spain. Ob- 
viously these vessels must have been rather small for ocean-going 
craft, unless there was more water in the San Juan River in those 
early days than at present. There are some obscure traditions 
of earthquakes having disturbed the bed of the river and made 
its passage more difficult by reducing the depth of water in 
some of the rapids ; but these reports are little more than tradi- 
tionary and lack authoritative confirmation. It is certain, how- 
ever, that the marine traffic, to which reference has been made, 
was maintained for a long period of years, its greatest activity 



392 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

existing at about the beginning of the seventeenth century. 
It was in connection with this traffic probably that the city of 
Granada at the northwestern extremity of the lake was estab- 
lished, perhaps before 1530. 

310. Early Examination of Nicaragua Route. — Although the 
apparently easy connection between the Caribbean Sea and Lake 
Nicaragua, together with the proximity of the latter to the Pacific 
coast, at once indicated the possibility of a feasible water com- 
munication between the two oceans, probably no systematic 
investigation to determine a definite canal line was made until 
that undertaken by Manuel Galisteo in 1779 under the instruc- 
tion of Charles III., who was then on the throne of Spain. Galis- 
teo made a report in 1781 that Lake Nicaragua was 134 feet 
higher than the Pacific Ocean, and that high mountains inter- 
vened between the lake and the ocean, making it impracticable 
to establish a water communiiation between the two. In spite 
of the discouragement of this report a company was subsequently 
formed under the patronag of the crown to construct a canal 
from Lake Nicaragua along the Sanoa River to the Gulf of Nicoya, 
but nothing ever came of the project. 

311. English Invasion of Nicaragua. — The cDuntry was in- 
vaded in 1780 by an English expedition sent out from Jamaica 
undr Captain Horatio Nelson, who subsequently became the 
great admiral. He proce ded up the San Juan River, and after 
some fighting captured by assault Fort San Juan at Castillo 
Viejo. Nelson and his force, however, were ill qualified to take 
care of themselves in that tropical country where drenching rains 
were constantly falling, and he was therefore obliged to aban- 
don his plan of taking possession of Lake Nicaragua and returned 
instead to Jamaica. The tropical fevers induced by exposure 
reduced the crew of his own ship, two hundred in number, to 
only ten after his return to Jamaica, and he himself nearly lost 
his life by sickness. 

312. Atlantic and Pacific Ship-canal Company. — Subsequently 
to this period the Nicaragua route attracted more or less attention 
until Mr. E. G. Squier, the first consul for the United States in 
Nicaragua, negotiated a treaty between the two countries for 
facilitating the traffic from the Atlantic to the Pacific Ocean by 



SURVEY AXD PROJECT OF COL. 0. W. CIIILDS. 393 

means of a shi]vcanal or railroad in the interest of the Atlantic 
and Pacific Ship-canal Company, composed of Cornelius Vander- 
bilt, Joseph L. White, Nathaniel Wolfe, and others. It was at 
this time that the Nicaragua route became prominent as a line 
of travel between New York and San Francisco. Ships carried 
passengers and freight from New York to Grey town, then trans- 
shipped them to river steamboats running up the San Juan River 
and across the southerly end of the lake to a small town called 
La Virgin, whence a good road for 14 miles overland led to the 
Pacific port of San Juan del Sur. Pacific coast steamships com- 
pleted the trip between the latter port and San Francisco. 

313. Survey and Project of Col. 0. W. Childs. — This traffic 
stimulated the old idea of a ship-canal across the Central Ameri- 
can isthmus on the Nicaragua route to such an extent that 
Col. O. W. Childs, an eminent civil engineer, was instructed by 
the American Atlantic and Pacific Ship-canal Company to make 
surveys and examinations for the project of a ship-canal on that 
route. The results of his surveys, made in 1850-52, have become 
classic in interoceanic canal literature. He concluded that the 
most feasible route lay up the San Juan River from Grey town 
to Lake Nicaragua, across that lake, and down the general course 
of the Rio Grande on the west side of Nicaragua to Brito on the 
Pacific coast. This is practically identical with the route adopted 
by the Isthmian Canal Commission now (1902) being discussed in 
Congress. 

314. The Project of the Maritime Canal Company. — The 
project planned by Col. Childs, hke those which preceded it, had 
no substantial issue, but the general subject of an isthmian canal 
across Nicaragua was, from that time, under almo t constant 
agitation and consideration more or less active until the Maritime 
Canal Company of Nicaragua was organized in February, 1889, 
under concessions secured from the governm.ents of Nicaragua and 
Costa Rica by Mr. A. G. Menocal. This company made a careful 
examination of all preceding proposed routes, and finally settled 
upon a plan radically different in some respects from any before 
considered. The Caribbean end of the canal was located on the 
Grey town Lagoon west of Grey town. From that point the line 
followed up the valley of the Deseado River and cut across the 



394 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



hills into the valley of the San Juan above its junction with the 
San Carlos. A dam was to be constructed across the San Juan 
River at Ochoa, below the mouth of the San Carlos, so as to bring 
the surface of Lake Nicaragua down to that point. From its 
junction with the San Juan River the canal line followed that 
river to the lake, across the latter to Las Lajas, and thence down 
the Rio Grande to the Pacific coast at Brito. It was contem- 
plated under this plan to carry the lake level to a point called 
La Flor, 13.5 miles west of the lake, and drop down to the Pacific 




Breakwater of the Maritime Canal Company. 
The closed former entrance to Greytown harbor is shown on the left. 



from that point by locks suitably located. After partially ex- 
cavating the canal prism for about three quarters of a mile from 
the Greytown Lagoon, constructing a line of railroad up the 
Deseado valley, as well as a telegraph line, and doing certain 
other work preparatory to the actual wo k of construction, the 
Maritime Canal Company became involved in financial difiiculties 
and suspended operations without again resuming them. 

315. The Work of the Ludlow and Nicaragua Canal Commissions. 
— In 1895 a-i^d again in 1897 two commissions were appointed by 
the President of the United States to consider the plans and esti- 



THE ROUTE OF THE ISTHMIAN CANAL COMMISSION. 395 

mates of the Maritime Canal Company in the one case, and the 
problem of a ship-canal on the Nicaragua route in the latter. 
Neither of these commissions, however, had the funds at its 
disposal requisite for a full and complete consideration of the 
problem. In 1899, therefore, the Isthmian Canal Commission 
was created by Act of Congress, and appointed by the Presi- 
dent of the United States, to determine the most feasible and 
practical route across the Central American isthmus for a 
canal, together with the cost of constructing it and placing it 
under the control, management, and ownership of the United 
States. This commission consisted of nine members, and in- 
cluded civil and military engineers, an ofihcer of the navy, an 
ex-senator of the United States, and a statistician. It was the 
province and duty of this commission to make examinations of 
the entire isthmus from the Atrato River in the northwestern 
corner of South Ameri'ca to the western limits of Nicaragua for 
the purpose of determining the most feasible and practical route 
for a ship-canal between those territorial limits. This brings the 
general consideration of the isthmian canal question to the Nica- 
ragua route in particular, to which alone attention will be directed 
in this part. 

316. The Route of the Isthmian Canal Commission. — The 
Isthmian Canal Commission adopted a route practically following 
the San Juan River from near Greytown to the lake, across the 
latter to Las Lajas on its westerly shore, and thence up the course 
of the Las Lajas River, across the continental divide into the 
Rio Grande valley, and down the latter to Brito at the mouth 
of the Rio Grande on the Pacific coast. As has already been 
stated, this is practically the line adopted by Col. Childs almost 
exactly fifty years ago. It is also essentially the route adopted 
by the Nicaragua Canal Commission appointed in 1897, and 
which completed its operations immediately prior to the creation 
of the Isthmian Canal Commission. The amount of work per- 
formed in the field under the direction of the commission can be 
realized from the statement that twenty working parties were 
organized in Nicaragua with one hundred and fifty-nine civil 
engineers and other assistants, and four hundred and fifty-five 
laborers. 



396 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



317. Standard Dimensions of Canal Prism. — By the Act of 

Congress creating it, the latter commission was instructed to 
consider plans and estimates for a canal of sufficient capacity to 
accommodate the largest ships afloat. In order to meet the 
requirements of those statutory instructions the commission 
decided to adopt 35 feet as the minimum depth of water in the 
canal throughout its entire length from the deep water of one 
ocean to that of the other, wherever the most feasible and practi- 
cal route might be located, the investigations of the commission 
having shown that the final location to be selected must narrow 
down to a choice between the Panama and the Nicaragua routes. 
It was further decided by the commission that the standard width 
of excavation at the bottom of the canal should be 150 feet, with 
500 feet for the ocean entrances to harbors, and 800 feet in 
those harbors. Greater widths than that of the bottom of stand- 
ard excavations were also adopted for river and lake portions. 



HARBOR SECTION 




7777777777777777777J77^777777^777^7^m^l 

Standard Sections adopted by the Isthmian Canal Commission. 

The slopes of the sides of the excavation were determined to be 
I vertical on i^ horizontal for firm earth, but as flat as i vertical 
on 3 or even 6 horizontal for soft mud or silt in marshy locations. 
In rock cutting below water the sides of the excavation would 
be vertical, but as steep as 4 vertical on i horizontal above water. 
The longest ship afloat at the present time (1902) is the 
Oceanic of the White Star Line, and its length is about 704 feet. 



THE SAN JUAN DELTA. 3U7 

The widest ships, i.e., the ships having the greatest beam, are 
naval vessels, and at the present time none has a greater beam 
than about 77 feet. In order to afford accommodation for 
further development in both length and beam of ships without 
leading to • extravagant dimensions, the commission decided to 
provide locks having a usable length of 740 feet with a clear 
width of 84 feet. These general dimensions meet fully the re- 
quirements of the law, and were adopted for plans and estimates 
on both the Panama and Nicaragua routes. 

318. The San Juan Delta. — The entire Central American 
isthmus is volcanic in character, and this is particularly true of 
the country along the Nicaragua route with the exception of the 
lowlands immediately back of the ocean shore-line in the vicinity 
of Grey town. From the latter point to Fort San Carlos, where 
the San Juan River leaves the lake, is approximately 100 miles. 
With the exception of the 15 miles nearest to the seacoast the 
San Juan River runs mostly through a rugged country with high 
hills densely wooded on either side. The soil is mostly heavy 
clay, although the bottom of the valley immediately adjacent to 
the river is largely of sandy silt with some mixture of clay. Be- 
tween the hi. Is back of Grey town and the seacoast the country 
is almost a continuous morass covered with coarse grasses and 
other dense tropical vegetation, but with a number of small 
isolated hills projecting up like islands in the surrounding marsh, 
and interspersed with numerous lagoons. All this flat country 
has the appearance of forming a delta through which a number 
of mouths of the San Juan River find their way. One of these, 
called the Lower San Juan, empties into the Grey town Lagoon, 
but the main mouth of the San Juan, called the Colorado, branches 
from the main river at the point where the Lower San Juan begins, 
about 13 or 14 miles from the ocean. The Colorado itself is 
composed of two branches, and at the place where it empties into 
the sea there are a number of long narrow lagoons parallel to 
the seashore, appearing to indicate comparatively recent shore 
formation. Again, a small river called the Rio San Juanillo leaves 
the main river 3 or 4 miles above the junction of the lower San 
Juan and the Colorado, and pursues a meandering course through 
the low marshy grounds back of Greytown, and finally again 



398 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



joins the Lower San Juan near the town. This marshy lowland 
is underlaid, by and formed largely of dark-colored sand brought 
down mostly from the volcanic mountains of Costa Rica by two 
rivers, the San Carlos and the Serapiqui, the former joining 
the San Juan about 44 miles and the latter about 23 miles from 
the sea. 




Greytown Lagoon (formerly Greytown Harl^or), showing Greytown in the Distance. 

319. The San Carlos and Serapiqui Rivers. — Both those Costa 
Rican rivers are subject to sudden and violent floods, and they 
bring down large quantities of this volcanic sand, the specific 
gravity of which is rather low. The San Carlos bears the 
greater burden of this kind. In fact its bed, even when not in 
a state of flood, is at many points at least composed of moving 
sands. Both rivers are clear-water streams except in high- 
water stages. Below the junction of the San Carlos the San Juan 
is necessarily in times of floods a large bearer of silt and sand, 
but above that point it carries little or no sediment. There are 
no streams of magnitude which join the San Juan between the 
lake and the San Carlos. 



THE RAPIDS AND CASTILLO VIEJO. 399 

320. The Rapids and Castillo Viejo. — About 54 miles from the 
ocean are the Machuca Rapids, and from that point to a distance 
of about 7 5 miles from the ocean other rapids are found, the prin- 
cipal of which are the Castillo and the Toro. The Castillo Rapids 
are at the -point called Castillo Viejo, where there is located an 
old Spanish fort on the top of the high hill around the base of 
which the river flows. The town of Castillo Viejo has a small 
population of perhaps 500 to 600 people. It is a place with his- 
torical associations, to which reference has already been made. 
It was here that Captain (afterwards Admiral) Nelson captured 
the Spanish fort in 1780. It is a place of some importance in 
connection with the river traffic in consequence of necessary 
transhipment of freight and passengers to overcome the rapids. 

321. The Upper San Juan. — The upper reaches of the San 
Juan within about 20 miles of the lake are bordered with con- 
siderable marshy ground. In the vicinity of its exit from the 
lake there is a wide strip of soft marshy country around the 
entire southeastern shore. 

322. The Rainfall from Greytown to the Lake. — The entire 
country between Greytown and the lake is intensely tropical, 
and the vegetation is characteristically dense. It is particularly 
so at Greytown, where the total annual rainfall sometimes reaches 
as much as 300 inches. It rains many times in a day, and nearly 
every day in the year. The strong easterly and northeasterly 
trade winds, heavy-laden with the evaporation from the tropical 
sea, meet the high ground in the vicinity of Greytown and pre- 
cipitate their watery contents in frequent and heavy showers. 
The general course of the San Juan valley is a little north of west 
or south of east, and the trade winds appear to f o low the course 
of the valley to the lake. The rainfall steadily decreases as the 
seashore is left behind, so that at Fort San Carlos, the point of 
exit of the river from the lake, the annual precipitation may vary 
from 75 to 100 inches. There is no so-called dry season between 
the lake and the Caribbean Sea, although at Fort San Carlos the 
rainfall is so small between the middle of December and the mid- 
dle of May that that period may perhaps be considered, rela- 
tively speaking, a dry season. It is evident, therefore, that all 
the conditions are favorable to luxuriant tropical growths over 



400 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



this entire eastern portion of the canal route, and the coarse 
grasses, palms, and other tropical vegetation found in it are inde- 
scribably dense. The same general observation is applicable to 
the forest and undergrowth throughout the entire course of the 
river from Greytown to Fort San Carlos. All of the high ground 
is heavily timbered, with undergrowth so dense that no survey 
line can be run until it is first completely cut out. That obser- 
vation holds with added force throughout the swampy country 




The Maritime Canal Company's Canal Cut leading out of Greytown Lagoon. 

adjacent to the seashore. All the heavy forest growth carries 
dense vines and innumerable orchids, which so cover the trunks 
and branches of trees as in many places completely to obscure 
them. 

323. Lake-surface Elevation and Slope of the River. — The 
lake surface has an area of about 3000 square miles and varies in 
elevation with the amount of rainfall in its basin from about 
97 or 98 to perhaps no feet above the ocean. The average ele- 
vation can probably be taken at about 104 feet above the sea. 
The length of the lake is about 103 miles, with a greatest width 
of 45 miles. The area of its watershed is about 12,000 square 



.Y.l 17G.1 770iV ON THE SAN JUAN. 401 

miles. Inasmuch as the length of the San Juan River from the 
ocean to the lake is but a little more than loo miles, its average 
fall is seen to be about i foot per mile. The greatest slope of 
the river surface is at Castillo Rapids, where it falls about 6 feet 
in § of a mile. At the Machuca Rapids it falls about 4 feet in 
I mile. From the foot of Machuca Rapids to the mouth of the 
San Carlos, a distance of a little over 15 miles, the surface of 
the river falls about i foot only. This pool, with practically no 
sensible current, is called Agua Muerte, or Dead Water. The 
relatively great depth of this pool shows conclusively that the 
upper San Juan, i.e., above the mouth of the San Carlos, carries 
no silt, otherwise the pool would be filled ; in other words, that 
part of the San Juan River is not a sediment-bearer. The slope 
of the river surface in the Toro Rapids, about 2 7 miles from the 
lake, gives a fall of 7to feet in i yV miles. 

324. Discharges of the San Juan, San Carlos, and Serapiqui. — 
In times of heavy floods the San Carlos River may discharge as 
much as 100,000 cubic feet per second into the San Juan, but 
such floods have a duration of a comparatively few hours only. 
Its low water-discharge may fall below 3000 cubic feet per sec- 
ond. The maximum outflow of the lake during a rainy season 
or a season of heavy rainfall probably never exceeds about 70,000 
cubic feet per second, but that rate of discharge may continue 
for a number of weeks. The low water-discharge of the San Juan 
above the mouth of the San Carlos may fall below 10,000 feet 
per second, or 13,000 feet per second below the mouth of the 
San Carlos but above that of the Serapiqui. 

325. Navigation on the San Juan. — From what has been said 
of the San Juan River it is evident that in times of low water no 
boats drawing more than about 5 or 6 feet can navigate it, and 
most of the river boats draw less than that amount. In times 
of low water no boat can navigate the Lower San Juan drawing 
more than about 2^ to 3 feet of water. Nor, again, can the ordi- 
nary river boats pass up the rapids at Castillo except at high water. 
It is necessary, therefore, that the larger boats used on the river 
confine their trips on the one hand between the mouth of the 
Colorado and Castillo, and on the other between Castillo above 
the rapids to Fort San Carlos. It is the custom, therefore, to 



402 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

transfer passengers and freight from boats below the rapids at 
Castillo by a short tramway to other boats in waiting above the 
rapids at that point. Boats pass up Machuca and Toro rapids 
at practically all seasons, but sometimes with difficulty. 

In order to meet the exigencies of low water in the Lower 
San Juan a railroad called the Silico Lake Railroad, with 3 feet 
gauge, has been constructed from a point opposite the mouth of 
the Colorado, called Boca Colorado, to Lake Silico in the marshes 
back of Grey town, a distance of about 6 miles. Light- draft boats 
connect Lake Silico with Greytown for the transfer of passengers 
and freight. The type of light-draft steamboat used on the San 
Juan River is the stern- wheel pattern, so much used on the west- 
em rivers of this country, the lower deck carrying the engines 
and boilers as well as freight, while the upper deck, fitted with 
crude staterooms, furnishes a kind of accom.modation for pas- 
sengers. 

326. The Canal Line through the Lake and Across the West 
Side. — The little town of Fort San Carlos on a point raised some- 
what above the lake where the San Juan River leaves the latter 
is the second place on the entire river from Greytown where any 
population may said to be found, and probably not more than 
400 or 500 people even there. Its position is on the north side 
of the river, at the extreme southeastern end of the lake, com- 
manding a fine view of the water and the country bordering it in 
that vicinity. To the westward lie the Solentiname Islands, a 
group a short distance to the north of which the sailing line for 
the canal in the lake is located. After passing this group of 
islands that line deflects a little toward the south, so that its 
course westward is but a little north of west, straight to a point 
near to and opposite Las Lajas on the westerly shore of the lake, 
southwest from the large island on which Ometepe and Madeira 
are located; indeed those two volcanic cones, the former still 
active, constitute the entire island. The point called Las Lajas 
is at the mouth of a small river of that name which discharges 
any sensible amount of water only during the wet season; it 
is located not more than 10 miles from Ometepe, and affords a 
most impressive view of that perfect volcanic cone rising almost 
an exact mile above the water. The general direction of the 



CHARACTER OF THE COUNTRY WEST OF THE LAKE. 403 

canal route is a little west of south from Las Lajas on the lake 
to Brito on the ocean shore. The line follows the Las Lajas 
about a mile and a half only of the 5 miles from the lake in a 
southwesterly direction to the point where the continental divide 
is crossed.- The elevation of the divide at this place is about 
145 feet only above sea-level. The line then descends immediately 
into the valley of the Rio Grande and follows that stream to its 
mouth at Brito. 

327. Character of the Country West of the Lake. — The coimtry 
on the west side of the lake exhibits a character radically different 
from that on the easterly side, i.e., between the lake and the 
Caribbean. It is a country in which much more population 
is found. While there are no towns along the 17 miles of the 




The Maritime Canal Company's Railroad near Greytown. 

route from Las Lajas to Brito, the old city Rivas, containing 
perhaps 12,000 to 15,000 people, is about 6 miles from Las Lajas, 
and the small towns of San Jorge, Buenos Ayres, Potosi, as well 



404 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

as others, are in the same general vicinity. Plantations of cacao 
and various tropical fruits abound, and there is a large amount 
of land under cultivation. It is largely a cleared country, so that 
far less dense forest areas are found. 

There are two distinct seasons in the year, the wet and the 
dry, the latter extending from about the middle of December 
to the middle of May. The annual rainfall is extremely variable, 
but in the vicinity of Rivas it may run from 30 or 40 to nearly 100 
inches. The country is of great natural beauty, and one which, 
under well-administered governmental control, would afford 
many places of delightful residence. The trade winds blow 
across the lake from east to west with considerable intensity 
and great regularity. They produce a beneficial effect upon the 
climate and render atmospheric conditions far more agreeable 
than in that part of Nicaragua in the vicinity of Grey town. 

It will be remembered that Rivas is the city where the Ameri- 
can filibuster Walker was taken prisoner by the Costa Ricans 
and Nicaraguans and shot in 1857. 

328. Granada to Managua, thence to Corinto. — At the north- 
western end of the lake is located the attractive city Granada, 
sometimes called the "Boston of Nicaragua." A reference to 
a map of Nicaragua will show that a short distance north of 
Granada is the river Tipitapa, which connects Lake Nicaragua 
with Lake Managua, the latter lying 18 miles to the northwest 
of the former. A railroad connects Granada with the city of 
Managua, which is the capital of Nicaragua, running on its way 
through the city of Masaya, chiefly noted for the volcano of the 
same name located near by, and which has been subjected to a 
most destructive eruption. The old lava-flow still shows its 
path of destruction by a broad black mark extending many miles 
across the country. A railroad connects Lake Managua at 
Momotombo with the Pacific port of Corinto. 

329. General Features of the Route. — It is thus seen that the 
proposed route of the Nicaragua Canal lies first along the valley 
of the San Juan River, then across the lake, cutting the con- 
tinental divide west of the latter at the low elevation of 145 feet 
above the sea, thence following the valley of the Rio Grande to 
the Pacific Ocean at Brito. From Greytown to Castillo the San 



ARTIFICIAL HARBOR AT GREY TOWN. 405 

Juan River is the boundary between Nicaragua and Costa Rica, 
and concessions from both governments would be necessary for 
that part of its construction. From Castillo to the Pacific Ocean 
the route lies entirely in Nicaraguan territory, and the only con- 
cession necessary fo ■ that portion of the line would be from the 
government of Nicaragua. From Castillo to and around the 
southern end of the lake the boundary-line is located 3 miles 
easterly from the river, fol owing its turns, and the same distance 
from the lake shore, all by an agreement recently reached between 
the two governments. The summit level of the canal would 
therefore be the surface of the water in Lake Nicaragua, which 
is carried down to Conchuda, 5 2 miles from the lake on the San 
Juan River toward the east, by a great dam located there, and 
to a lock between 4 and 5 miles from the lake toward the west. 
Hence the summit level would stretch throughout a distance 
of about 126 miles, leaving a little more than 46 miles on the 
Caribbean end and about 1 2 miles on the Pacific end of the regular 
canal section. The 50-mile stretch from the lake to the point 
where the canal cuts the San Juan River near Conchuda is a 
canalized portion of the San Juan River, as a large amount of 
excavation must be done there in order to give the minimum 
required depth of 35 feet. The points of river bends or curves 
are in some cases cut off by excavated canal section in order to 
shorten the line and reduce the curvature. Considerable por- 
tions of the line in the lake, particularly near Fort San Carlos, 
would be excavated. For several miles in the latter vicinity 
large quantities of silt and mud must be removed, as the lake 
is shallow and the bottom is very soft. The entrance into the 
western portion of the canal at Las Lajas requi es a large amount 
of rock excavation, as the shore and bed of the lake there are 
almost entirely of rock. 

330. Artificial Harbor at Greytown. — The preceding obser- 
vations are mostly of a general character, and give but little 
consideration to the engineering features of the canal construc- 
tion. In considering the canal as a carrier of ocean traffic 
probably the first inquiry will be that relating to harbors. In 
reality there is no natural harbor at either end of the Nicaragua 
route. Fifty years ago there was an excellent harbor at Grey- 



406 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



town into which ships drawing as much as 30 feet found ready 
entrance, and within which was afforded a well-protected an- 
chorage. As early as that date, however, a point of land or 
sand-pit was already pushing its way northward in consequence 
of the movement of the sand along the beach in that direction, 
and in 1865 it had nearly closed the entrance to the harbor. 




Scene on the San Juan River. 

For many years that entrance has been entirely closed, and now 
what was once the protected harbor of Greytown is a shallow 
body of water, completely closed, and known as the Greytown 
Lagoon. There is a narrow, circuitous, and shallow channel 
leading from it out to an opening in the sand-bar, which may be 
navigated by boats drawing not more than 2 or 3 feet, and by 
means of which freight and passengers are taken from steamers, 
which are obliged to anchor in the offing. Occasionally heavy 
storms break through this strip of sand between Greytown 
Lagoon and the ocean, and for a short time form a shallow en- 
trance to the former. The sand movement in that vicinity 
northward or westward is so active that it is but a short time 
before such openings are again closed. The deepest water in 
the lagoon probably does not exceed 8 or 10 feet at the present 



ARTIFICIAL HARBOR AT BRITO. 407 

time, and the most of it is much shallower. The tidal action at 
Greytown is almost nothing, as the range of tide between high 
and low is less than i foot. The mean level of the Caribbean 
Sea is the same as that of the Pacific Ocean. 

Under tliese circumstances it is necessary to create what is 
practically a new harbor at Greytown, and that work is con- 
templated in the plans of the Isthmian Canal Commission. The 
canal line is foimd entering the lagoon about i mile northwest 
of Greytown, where a harbor is planned having a length of 2500 
feet and a width of 500 feet, increased at the inner end to 800 feet 
to provide a turning-basin. The entrance to this harbor from 
the ocean will be dredged to a width of 500 feet at the bottom, 
and it will be protected outside of the beach-line by two jetties, 
the easterly about 3000 feet long, and the westerly somewhat 
shorter. These jetties would ' ' be built of loose stone of irregular 
shape and size, resting on a suitable foundation," the largest, 
constituting the covering, weighing not less than 10 to 15 tons 
each. These jetties would be carried 6 feet above high water 
and have a top width of 20 feet. The trade winds, which blow 
from the easterly and northeasterly, would have a direction 
approximately at right angles to that of the easterly jetty, and 
ships making the entrance of the canal would consequently be 
protected against them while between the jetties. The easterly 
of these jetties would act as an obstruction against the westerly 
movement of the sand, but it is practically certain that a con- 
siderable amount of the latter would be swept into the channel, 
and possibly to some extent into the harbor, necessitating dredg- 
ing a considerable portion of the time. The commission estimates 
that the maintenance of the entrance and harbor would require 
an annual expenditure of $100,000. 

331. Artificial Harbor at Brito. — The harbor at Brito presents 
a problem of a different kind. There is absolutely no semblance 
of a harbor there at the present time (1902) ; it is simply a location 
on the sandy beach of the ocean protected against swells from 
the west by a projecting rocky point called Brito Head, the Rio 
Grande River emptying into the ocean just at the foot of Brito 
Head, between it and the canal terminus. The entire harbor 
and its entrance would be excavated in the low ground of that 



408 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

vicinity, composed mostly of sand and silt, although there would 
be a little rock excavation. The entrance to the harbor would 
be dredged 500 feet wide at the bottom, and be protected by a 
single jetty on the southeasterly side. The harbor itself would 
be excavated back of the present beach ; it would have a length 
of 2200 feet and a width of 800 feet. As the depth of water 
increases rather rapidly off shore, the lo-fa thorn curve is found 
at about 2200 feet from low-water mark, hence the jetty would 
not need to be more than probably 1800 to 2000 feet long. In 
this vicinity the water is usually smooth ; indeed but few storms 
annually visit this part of the coast. The conditions are quite 
similar to those found on the coast of Southern California. There 
is little sand movement in this vicinity, and the annual expen- 
ditures for maintenance of the harbor and entrance would be 
relatively small; the commission has estimated them at $50,000. 
332. From Grey town Harbor to Lock No. 2. — The canal line, 
on leaving the harbor at Greytown, is found in low marshy ground 
for a distance of about 7 miles, the excavation being mainly 
through the sand, silt, mud, and vegetable matter characteristic 
of that location. Throughout almost this entire distance the 
natural surface is but little above sea-level. The first ground 
elevated much above this marshy country is known as the Mis- 
terioso Hills, in which Lock No. i is founded, having a lift of 
36^ feet and raising the water surface in the canal by that amount 
above sea-level. Another stretch of marshy country, .but not 
quite so wet as the preceding, follows for a distance of about 1 1 
miles, when the Rio Negro Hills rise abruptly to an elevation of 
a little over 150 feet above sea-level. At this point is located 
Lock No. 2, with a lift of i8| feet. This lock is about 21 miles 
from the 6 -fathom line off Greytown. The canal line here prac- 
tically reaches the San Juan River, the latter lying a considerable 
distance easterly of the canal, between this point and the ocean. 
Between Greytown and Lock No. 2 embankments, never reaching 
a greater height than 10 to 15 feet, are required to keep the water 
in the canal at various locations along the low ground. These 
embankments do not necessarily follow parallel to the centre 
line of the canal route, but are planned to connect hills, or rather 
high ground, so as to reduce their length and give them a more 




Approach Wall 
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SECTION ON LINE B-B 






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FROM LOCK NO. 2 TO THE LAKE. 



409 



stable character than if they were located close to the canal ex- 
cavation. While some embankments will still be found above 
Lock No. 2, they are few, and even lower than those already 
noticed. From Lock No. 2 to Lake Nicaragua the route of the 
canal lies practically along the San Juan River, the chief excep- 




Telegraph Office at Oclioa on the San Juan River. 

tion to that statement being the cut-off in the vicinity of the 
Conchuda dam. 

333. From Lock No. 2 to the Lake.— Inasmuch as both the 
Serapiqui and San Carlos rivers flow from Costa Rican territory 
into the San Juan, that is, from its right bank, the canal line neces- 
sarily is located along the northerly or left bank of that river. At 
a distance of 23 miles from the ocean the canal line cuts through 
what are called the Serapiqui Hills opposite the mouth of the 
river of that name, and at a distance of a little over 26 miles 
from the ocean it pierces the Tamborcito Ridge, where is found 
the deepest cutting on the entire route. The total length of 



410 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

cut through this ridge is about 3000 feet, but its greatest depth 
is 297 feet, and it consists largely of hard, basaltic rock. The 
next lock, or Lock No. 3, is found about 17 miles from Lock 
No. 2, or 38 miles from the sea, and it has, like Lock No. 2, a 
lift of i8-| feet, raising the surface of the water in the canal to an 
elevation of 73^ feet above the sea. Continuous heavy cutting 
through what are called the Machado Hills brings the line to 
Lock No. 4, at a distance of a little less than 41 miles from the 
ocean. This lock has a lift varying from 30.5 to 36.5 feet, inas- 
much as it raises the surface of the water in the canal to the sum- 
mit level in the lake. The maximum lift of 36.5 feet would 
be required when the lake level stands at an elevation of 1 10 feet 
above the sea, and 30.5 feet when the same surface stands at an 
elevation of 104 feet above the sea. Although the water surface 
in the canal level above this lock is identical with the summit 
level in the lake, the canal line again runs through continuous 
heavy cutting for a distance of 5 miles before it reaches the canal- 
ized San Juan. This portion of the line between Lock No. 4 
and the San Juan River is called the Conchuda cut-off, for the 
reason that the point called Conchuda, where the great dam is. 
located, is but 3 miles down the river from the point where the 
canal enters it. From Conchuda to the lake, as has already 
been stated, the canal line follows the course of the San Juan 
River, which must be canalized by considerable excavation of 
earth and rock, both along the bed and in cut-offs. The greater 
part of this cutting must obviously be on that portion of the 
river toward the lake, as that is the highest part of the river-bed 
in its natural condition. 

334. Fort San Carlos to Brito. — The distance from the point 
of entrance of the canal into the San Juan River near Conchuda 
to Fort San Carlos on the shore of Lake Nicaragua is about 50 
miles, while the distance across the lake on the canal line is 70.5 
miles, which brings the line to Las Lajas on the southwesterly 
shore of the lake. 

There is considerable heavy cutting through the continental 
divide between the lake and the first lock westerly of it, i.e., Lock 
No. 5. The maximum cutting is but 76 feet in depth, and the 
average is but little less than that for nearly 3 miles. This lock 



EXAMINATIONS BY BORINGS. 



411 



is located a little less than lo miles from the lake and nearly 176 
miles from the 6-fathom line off Greytown. The place at which 
this lock is located is known as Buen Retiro. The lift of Lock 
No. 5 varies from 28-^ feet as a maximum to the minimum of 22^ 
feet, bringing the water surface in the canal down to 81^ feet 
above mean ocean level. Lock No. 6 is located but about 2 miles 
west of Lock No. 5, and also has a lift of 28^ feet. The line now 




Surveying Party of the Isthmian Canal Commission on the San Juan River. 

runs along the course of the Rio Grande to the ocean, Lock No. 7 
being also 2 miles west of Lock No. 6, again with a lift of 28^ feet. 
The last lock on the line, or Lock No. 8, but a mile from the Pacific 
Ocean, and about 182 miles from the Caribbean Sea, has a maxi- 
mum lift of 28^ feet, and a minimum lift of 20+ feet, the range 
of tide in the Pacific Ocean being but 8 feet at Brito. There 
are thus four locks between the lake and the Pacific Ocean, each 
having a possible lift of 28^ feet. 

The entire distance between the 6-fathom lines in the two 
oceans is 183.66 miles. 

335. Examinations by Borings. — Obviously it is of the great- 
est importance that such structures as the locks and dams re- 
quired in connection with this canal route should be founded on 



412 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

bed-rock. In order to determine not only such questions, but 
the character of all materials to be excavated from one end of the 
route to the other, a great number of borings were made along 
the canal line, not only by the water-jet process, but also with 
the diamond drill. By means of the latter, whenever it was so 
desired, cores or circular pieces could be taken out of the bed-rock 
so as to show precisely its character at all depths. These borings, 
both through earthy material by the jet and into bed-rock by 
the diamond drill, were made at suitable distances apart along 
the centre line of the canal, and in considerable numbers, closer 
together at proposed lock and dam sites. By these means every 
lock on the line has certainly been located on bed-rock, as well 
as the great dam at Conchuda. In addition to this the commis- 
sion has been able to classify the material to be excavated, so 
that if the canal should be built every contractor would know 
precisely the character and quantity of the various materials 
which he would have to deal with. 

336. Classification and Estimate of Quantities. — The following 
table is arranged to exhibit a few only of the principal items of 
excavation, so as to give an approximate idea at least of the 
magnitude of the work to be done: 

Dredging ■ • • 130,920,905 cu. yds. 

Dry earth 47,440,316 

Soft rock 14,029,170 

Hard rock 24,151,214 

Rock under water 2,780,040 

Embankment and back-filling 8,389,960 

Clearing • . 6,831 acres. 

Stone-pitching 250,089 sq. yds. 

Concrete, excluding retaining-walls 3,400,840 cu. yds. 

Concrete in retaining-walls 424,321 

Cut stone 22,272 

Steel and iron, excluding cast-iron culvert lining 61,735,230 lbs. 

Cast-iron culvert lining 19,286,000 

Brick culvert lining 34,542 cu. yds. 

Cost of lock machinery $1 ,600,000 

Excavation in coffer-dam 9,907 cu. yds. 

Pneumatic work 145-557 

Piling 415,600 lin. ft. 

Rock fill in jetties 451,5°° cu. jds. 

Clay puddle, bottom and sides of canal 936,800 



CLASSIFICATION AND UNIT PRICES. 413 

337. Classification and Unit Prices. — The classification of the 
material to be excavated, both on the Nicaragua and Panama 
routes, was one to which the commission gave very thoughtful 
study no less than to the prices to be used in making the esti- 
mates. The following table, taken from pages 67 and 68 of the 
commission's report, exhibits the classification and the prices 
adopted by the commission for purposes of its estimates: 

Removal of hard rock, per cu. yd $1 • 15 

Removal of soft rock, per cu. yd .80 

Removal of earth, not handled by dredge, per cu. yd .4? 

Removal of .dredgable material, per cu. yd .20 

Removal of rock, under water, per cu. yd 4-75 

Embankments and back-filling, per cu. yd .60 

Rock in jetty construction, per cu. yd 2 . 50 

Stone-pitching, including necessary backing, per sq. yd 2 . 00 

Clearing and grubbing in swamp sections of Nicaragua, per acre.. . . 200 . 00 

Other clearing and grubbing on both routes, per acre 100 .00 

Concrete, in place, per cu. yd 8 . 00 

Finished granite, per cu. yd 60 . 00 

Brick in culvert lining, per cu. yd 15 . 00 

All metal in locks, exclusive of machinery and culvert linings, per lb. .075 

All metal in sluices, per lb .075 

Cast iron in culvert lining, per lb .04 

Allowance for each lock-chamber for operating machinery 50,000 . 00 

Additional allowance for each group of locks for power-plant 100,000 . 00 

Price of timber in locks, per M B. M 100 . 00 

Sheet-piling in spillways, per M B. M 75 • 00 

Bearing piles in spillways, per lin. ft .50 

Average price of pneumatic work for the Bohio dam, below eleva- 
tion— 30, per cu. yd 29 . 50 

Caisson work for the Conchuda dam, in place, per cu. yd 20.00 

Single-track railroad complete with switches, stations, and rolling 

stock, per mile of main line 7 5, 000 . 00 

There are evidently other more or less uncertain expenditures, 
depending upon all possible conditions affecting the cost of such 
work, including those of climate, police, and sanitation. In 
order to cover such expenditure the commission determined to 
add 20 per cent to all its estimates of cost on both routes, and 
that percentage was so added in all cases. 

338. Curvature of the Route. — Among the engineering fea- 
tures of a ship-canal line it is evident that curvature is one of 
great importance. Small steam-vessels may easily navigate 
almost any tortuous channel, but it is not so with great ocean 



414 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



steamships. On the other hand, it may require very deep and 
expensive cutting to reduce the curvature of the route, as curves 
are usually introduced to carry the line around some high ground. 
It is necessary, therefore, to make a careful and judicious balance 
between these opposing considerations. The commission wisely 




Boring Party of the Isthmian Canal Commission on a Raft in the San Juan River. 

decided to incur even heavy cutting at some points for the purpose 
of avoiding troublesome curvature on the Nicaragua route. The 
table on page 415, taken from page 135 of the commission's 
report, gives all the elements of curvature for the entire line. 

From the description of the line as given, it is evident that 
much curvature must be found in spite of the most judicious 
efforts to avoid it, and the table indicates that condition. Yet 
the amount of curvature may be considered moderate for a loca- 
tion through such a country as Nicaragua. The smallest radius 
is seen to be a little over 4000 feet. The result may be considered 
satisfactory for such a difficult canal country, although the total 
amount of curvature is rather formidable. 

339. The Conchuda Dam and Wasteway. — The most impor- 
tant single engineering feature of the whole plan is the dam at 
Conchuda. The ordinary low-water elevation in the river at 



THE CONCIIUDA DAM AND WASTEWAY 



415 



Number of 
Curves. 

. 


Radius. 


Length. 


Total Degrees of 
Curve. 




Feet. 


Miles. 





2 


17,189 


^■53 


26 51 10 


8 


11,459 


6.80 


179 31 50 


4 


8,594 


4.31 


151 40 50 


1 


8,385 


1-43 


51 44 30 


2 


7,814 


I .90 


73 28 30 


I 


7,759 


1-73 


67 16 50 


5 


6,876 


4.64 


204 34 40 


2 


5,927 


2 .40 


122 41 20 


i6 


5,730 


II .08 


584 47 40 


2 


5,289 


2.27 


129 45 50 


I 


5,209 


1-15 


66 38 30 


2 


5,056 


1 .22 


73 17 40 


I 


4,982 


.82 


49 49 00 


3 


4,911 


2-75 


169 36 00 


I 


4,297 


•63 


44 19 50 


I 


4,175 


.81 


58 20 40 


4 


4,04s 


3.82 


285 25 40 


56 




49.29 


2,339 50 30 



the dam site may be taken at about 55 feet above the sea. Inas- 
much as the greatest elevation of the water in the lake is supposed 
to be about no feet, it will be seen that its surface will be but 
55 feet above the present elevation, making its maximum depth 
at that point about 105 feet if there should be no fill on the up- 
stream side of the dam, inasmuch as the present depth of water 
in the river at the stage assumed is about 50 feet. 

This dam would be a structure of concrete masonry with cut- 
stone facing only at a few points where it would be advisable to 
use that material. A large part of the flood discharge, or the 
discharge of other surplus water, would be made over a properly 
designed crest of the dam ; hence its outline would be that shown 
in the accompanying figure, shaped so as to prevent the over- 
flowing sheet of water from damaging the structure. This dam 
will be founded upon pneumatic caissons, and the borings made 
by the commission show that the deepest of them would reach 
satisfactory bed-rock at no greater depth than 25 feet below sea- 
level, or about 80 feet below the ordinary stage of water in the 
river. The construction of this dam therefore w^ould involve 
no unusual operations, but it would all be performed within the 
more usual and easy limits of the pneumatic process of con- 



416 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



structing foundations. The masonry crest of this dam would 
be finished at the elevation of 97 feet above sea-level, or about 
13 feet below the highest elevation of water in the lake. The 
length of that part of this masonry dam, located on pneumatic 
caissons, would be 731 feet, but the total length of the entire 
masonry structure would be 13 10 feet. The total length of crest, 




Castillo Viejo, on the San Juan River, about thirty -seven miles from the lake and at the 
Castillo Rapids. The old fort is shown on the right at the summit of the hill. 

including the masonry piers on it, over which the surplus waters 
would flow, would be 810 feet, but there ara twenty piers 9 feet 
thick, so that the net len;5th of crest available for overflow of 
waste-waters would be about 630 feet. The piers to whi«h refer- 
ence is made are those required for the support of the movable 
gates of the Stoney type which would be employed to regulate 
the discharge over the dam. The maximum elevation of the 
tops of these piers' required for the support and operation of the 
Stoney gates is 132 feet above sea-level. The masonry dam 
thus furnished with movable gates can be used in times of flood 
to prevent the water of the lake rising above about no feet above 
sea-level. In times of low rainfall or during the dry season the 
gates would prevent the escape of water needed for storage. 

The total available length of crest on this masonry dam is 
not sufficient to exercise all the control that is needed to keep 



REGULATION OF THE LAKE LEVEL. 417 

the lake within desired hmits, and the commission was obHged 
to avail itself of a low depression or saddle between the hills less 
than a half-mile easterly of the dam site. The depression affords 
an additional total length of crest of 1239 feet, or, taking out 
thirty-one piers, each 9 feet wide, a net available length of 960 
feet, making in combination with the crest of the main dam a 
total net available length of 1590 feet. The total wastage over 
these two structures, i.e., the main dam at Conchuda and the 
Conchuda wasteway on the Costa Rican side of the river, may 
be at the rate of 100,000 cubic feet per second, with a maximum 
depth over the crest of 7 feet, which is sufficient to meet the 
demands of the heaviest rainfall in the lake basin. 

The plans and elevations on pages 421, 423, and 424 show all 
the main features of both the Conchuda dam and wasteway as 
designed by the commission. 

340. Regulation of the Lake Level. — One of the most impor- 
tant engineering questions connected with the consideration of 
the Nicaragua route is that of the regulation or control of the 
surface of the water in Lake Nicaragua constituting the summit 
level of the canal. 

As has already been stated, the drainage-basin of the lake, 
about 12,000 square miles in area, is subjected to an annual wet 
season extending from about the middle of May to the middle of 
December, the dry season extending over the remaining portion 
of the year. The average annual rainfall over the entire lake 
basin is not accurately known, although the Isthmian Canal 
Commission maintained rainfall records at several points on the 
lake shore and at other points in the basin dtiring periods of i|- 
to 2 years, and records running back over periods of perhaps 
12 to 15 years are available from Rivas, Granada, and Masaya. 
Fortunately, also, both the Nica agua and the Isthmian Canal 
Commissions maintained gauging-stations at various points on 
the San Juan throughout the periods of service of these com- 
missions, so that the discharges of the river could be known from 
accurate measures at various seasons for at least two or three 
years. These observations, although not as extended as could 
be desired, yield sufficient data for a comparatively thorough 
treatment of the subject of lake-surface control. 



418 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

Obviously throughout the rainy season of the year, except 
during years of low rainfall, some water would necessarily be 
wasted from the lake because its retention would raise the surface 
of the lake too high, causing damage, floods, or injurious over- 
flows at various places around the lake shore. On the other 
hand, unless some water were stored from the rainy periods or 
wet seasons there would not be sufficient in the lake to supply 




Village of Fort San Carlos at Entrance to the San Juan River. Lake Nicaragua is on 
the right and San Juan River in the middle ground. 

during the dry period of the year, or during low rainfall years, 
the requisite quantity for the wastage of evaporation from its 
surface and for the operation of the canal, and at the same time 
maintain the minimum depth of water of 35 feet required in 
the canal. It was necessary, therefore, to design at least the gen- 
eral features of such regulating-works as would prevent the lake 
from rising too high in wet periods, and from falling too low in 
dry periods or low rainfall years. 

341. Evaporation and Lockage. — The observations of both 
commissions show conclusively that the average evaporation 
from the surface of Lake Nicaragua is about 60 inches or 5 feet 
per year, varying from perhaps a maximum of 6 inches per month 
to a minimum of possibly about 4 inches per month. Further- 
more, careful estimates of the quantity of water required for the 



REQUIRED SLOPE OF THE CANALIZED RIVER SURFACE- 419 

purposes of the canal, on the supposition that about 10,000,000 
tons of traffic would pass through it annually, including lockage, 
leakage through the gates of the locks, evaporation, power pur- 
poses, and other incidentals, show that about 1000 cubic feet of 
water per second must be provided. Whatever maybe the char- 
acter of the season, therefore, there must be at least sufficient 
water stored in the lake to provide for the wastage of evaporation 
from the lake and canal surfaces and for the proper operation of 
all the locks throughout the length of the canal. The super- 
ficial area of Lake Nicaragua is but little less than 3000 square 
miles. The quantity of water required for the operation of the 
canal, amounting to 1000 cubic feet per second, would, for the 
entire year, make a layer of water over the lake surface of less 
than 5 inches in thickness. In other words, the operation of the 
canal, for a traffic of about 10,000,000 tons annually, requires 
an amount of water less than one twelfth of that which would 
be evaporated from the lake surface during the same period. 

342. The Required Slope of the Canalized River Surface. — 
The dam located at Conchuda and fitted with suitable movable 
gates affords means of accomplishing the entire lake-surface 
control. That dam is located, however, nearly 53 miles from 
the lake, and in order that the requisite discharge may take place 
over it during the rainy season there must be considerable slope 
of the water surface in the canalized river from the lake down 
to the dam. It was necessary, therefore, to compute that slope, 
from data secured by the commission, with the lake surface at 
various elevations between the minimum and maximum per- 
mitted. These slopes were found to be such that the difference 
in elevations of the surface of the water at the dam and in the 
lake might vary from about 6 to 9 feet, those figures representing 
the total fall for the distance of 53 miles. 

343. All Surplus Water to be Discharged over the Conchuda 
Dam. — The Nicaragua Commission contemplated the construc- 
tion of dams not only on the San Juan River at Boca San Carlos, 
about 6 miles below Conchuda, but also another a few miles west 
of the lake at La Flor, so as to discharge the surplus waters at 
both points, but by far the largest part over the dam at Boca 
San Carlos. The Isthmian Canal Commission, however, decided 



420 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

to build no dam on the west side of the lake, but to discharge all 
the surplus waters over the dam at Conchuda. 

344. Control of the Surface Elevation of the Lake. — The rain- 
fall records in the lake basin have shown that a dry season begin- 
ning as early as November may be followed by an extremely low 
rainfall period, which in turn would be followed by a dry season 
in natural sequence, lasting as late as June. It may happen, 
therefore, that from November until a year from the succeeding 
June, constituting a period of nineteen months, there will be a 




The Active Volcano Ometepe in Lake Nicaragua, showing Clouds on Leeward Side of 
the Summit. The crater is nearly eleven miles from the canal line. 

very meagre rainfall in the lake basin, during which the precipi- 
tation of the seven low rainfall wet months may not be sufficient 
even to make good the depletion of evaporation alone during 
the same period. It would be necessary, then, at the end of any 
wet season whatever, i.e., during the first half of any December, 
or in November, to make sure of sufficient storage in the lake 
to meet the requirements of the driest nineteen months that can 
be anticipated. That condition was assumed by the commission, 
and the elements of control of the lake surface, in its plans, are 



CONTROL OF THE SURFACE ELEVATION OF THE LAKE. 421 




422 THE NICARAGUA ROUTE FOR A SHIP-CANAL. 

such as to afford resources to meet precisely those low- water con- 
ditions. 

The commission's study of these features of the Nicaragua 
Canal problem resulted in plans of works to prevent the surface 
of the lake ever falling below 104 feet above sea-level, or rarely 
if ever rising higher than the elevation of 1 1 o feet above the same 
level, thus making the possible range of the lake surface about 
6 feet between its lowest and its highest position. 

Obviously at the end of a dry season the gates at the dam 
will always be found closed, and there will be no water escaping 
from the lake except by evaporation and to supply the needs of 
canal operation. It is equally evident that the gates will also 
remain closed so as to permit no wastage during the early part 
of the wet season. As the wet season proceeds the surface of- the 
lake will rise toward, and generally quite to its maximum eleva- 
tion ; the operation of wasting over the weirs will then commence. 
The time of beginning of this wastage will depend upon the 
amount and distribution of the rainfall during the wet period. 
Indeed no wastage whatever would be permitted during such a 
low-water wet season as that shown by the records of 1890, which 
was almost phenomenal in its low precipitation. The rainfall 
for the entire drainage-basin would be impounded in the lake in 
that case, and it would then fall short of restoring the depletion 
resulting from evaporation and requirements of the canal. On 
the other hand, during such a wet season as that of 1897 wastage 
would begin at an early date. In general it may be said that 
neither the rate nor the law of the rise of water surface in the lake 
can be predicted. There will be years when no wastage will be 
permitted, but generally considerable wastage will be necessary 
in order to prevent the lake rising above the permissible highest 
stage. 

Detailed computations based upon the statistics of actual 
rainfall records in the basin of Lake Nicaragua may be found by 
referring to pages 147 to 152 of the Report of the Isthmian Canal 
Commission, and they need not be repeated here. Those com- 
putations show among other things that October is often a month 
of excessive rainfall, and that the greatest elevation of the lake 
surface is likely to follow the precipitation of that month. Hence 



CONTROL OF THE SURFACE ELEVATION OF THE LAKE. 423 



the greatest discharge of surplus waters over the Conchuda dam 
may be expected in consequence of the resuhing run-off or inflow 



•Tj 



O 




into the lake. Those computations also show that at long inter- 
vals of time the lake surface might reach an elevation of nearly 



424 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



112 feet above sea-level for short periods, causing the discharge 
in the canalized river or over the Conchuda dam to reach possibly 
76,000 cubic feet per second, the elevation of the water at the 
dam being 104 feet above sea-level. Furthermore, the Sabalos 
River and one or two other small streams, emptying into the San 
Juan above the dam, might concurrently be in flood for at least 
a few hours and augment the discharge over the dam to 100,000 
cubic feet per second. The regulating-works at the dam, con- 
sisting of the movable (Stoney) gates, were devised by the com- 
mission to afford that rate of discharge, an aggregate net or avail- 
able length of overflow crest at the dam and waste way of 1590 
feet being necessary for that purpose with a depth of water on 
the crest not exceeding 7 feet. 



-f-llOHlgh Water 



+104i.ow Water 



+132' 

67" 



+113 



CONCHUDO DAM. 

SECTION SHOWING 
CAISSONS 




No's 5.6-9, 95 Ft. •- 



~ . No's 7:8, 102 Ft. 



CONCHUDO DAM 

DIAGRAM 

SHOWING ARRANGEMENT 

OF SLUICE GATE 




The commission states on page 156 of its report : 
While, therefore, no detailed instructions can be set forth 
regarding the condition of the sluices at the wasteway on specified 
dates, the general lines of their operation should be stated below, 
viz. : 



GREATEST VELOCITIES IN CANALIZED RIVER. 



425 



" I. A full lake with surface probably a little above no feet 
on December i. 

" 2 . Wasteway sluices closed at least from about December i 
to some date in the early portion of the succeeding rainy season, 
or throughout that season if it be one of unusually low precipi- 
tation. 

"3. A variable opening of wasteway sluices, if necessary, 
during the intermediate portion of the rainy season, so as to main- 
tain the lake surface elevation but little, if any, below no at the 
beginning of October. 

' ' 4, The operation of wasteway sluices during October and 
November so as to reach the ist of December with a full lake, 
or lake elevation p obably a little above no feet." 

It is thus seen that while the measures for control and regula- 
tion are entirely feasible, they are not sharply defined, nor so sim- 
ple that some experience in their ope ation might not be needful 
for the most satisfactory re ults. 

345. Greatest Velocities in Canalized River. — It is necessary 
to ascertain whether the velocities induced in the canalized por- 
tions of the San Juan Rive would not be too high for the con- 
venience of traffic during the highest 1 ainfall season. The following 
table and the succeeding paragraph, taken from the commission's 
report, show that no sensible difficulty of this kind would exist. 





Elevation of Water at Dam. - 


Elevation of Lake. 


103 Feet. 


104 Feet. 


Feet. 
no 
III 
112 


Feet per Second. 
4 . 16 

4.51 

4.85 


Miles per Hour. 

2.8 

3-1 
3-3 


Feet per Second. 
3-9 
4.2 

4-5 


Miles per Hour. 
2.7 
2.9 
3-1 



The discharge of the river corresponding to the velocity of 
2.7 miles per hour is 63,200 cubic feet per second; while that 
corresponding to 3.3 miles per hour is 77,000 cubic eet per second. 
These estimated high velocities will occur but rarely, and they 
will not sensibly inconvenience navigation. In reality they are 
too high, for the reason that while the overflow at the minimum 



426 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 




WASTEWAYS OR OVERFLOWS. 427 

river section materially increases the areas of those sections, it 
has been neglected in this discussion." 

346. Wasteways or Overflows. — At a number of places on the 
route there are some small streams which must be taken into 
the canal, and which when in flood require tha certain waste- 
ways or overflows from the canal prism should be provided at 
or near where such streams are received. These wasteways are 
simply overfall-weirs with the crests at the elevation of the lowest 
water surface in the canal prism. The principal works of this 
kind are on the east side of the lake and involve a total drainage 
area or area of watershed of about 107 square miles. Ample 
provision has been made by the commission for all such struc- 
tural features. 

347. Temporary Harbors and Service Railroad. — Before actual 
work could be begun at either end of the Nicaragua route tem- 
porary harbors would have to be constructed both at Greytown 
and at Brito to enable contractors to land plant and supplies 
or other material. These temporary harbors would probably 
require no greater depth of water than 18 feet, but they would 
be works of considerable magnitude, and provision was made for 
them in the commission's estimate of cost. Again, a service rail- 
road of substantial character would have to be built from Grey- 
town up to Sabalos, approximately half-way between the Con- 
chuda dam and Fort San Carlos, as well as from the west shore 
of the lake to Brito, making a total line of about 100 miles. The 
commission estimated the cost of this railroad and its rolling 
stock at $75,000 per mile. 

348. Itemized Statement of Length and Cost. — The following 
table gives the lengths of the various portions of the canal and the 
principal items of its cost, so arranged as to show the classifica- 
tion of the various items of the total sum to be expended for all 
purposes during the construction of the entire work. 

The commission estimated the total time required in preparing 
for and performing the actual construction of the work at eight 
years, but the writer believes that at least two years more should 
be allowed for the work. 



428 



THE NICARAGUA ROUTE FOR A SHIP-CANAL. 



Miles. 



Cost. 



Greytown harbor and entrance 

Section from Greytown harbor to lock No. i, including 
approach-wall to lock 

Diversion of Lower San Juan 

Diversion of San Juanillo 

Lock No. I, including excavation 

Section fromlockNo. i to lock No. 2, including approach- 
walls, embankments, and wasteway 

Lock No. 2, including excavation 

Section from lock No. 2 to lock No. 3, including approach- 
walls, embankments, and wasteway 

Lock No. 3, including excavation 

Section fromlockNo. 3 to lock No. 4, including approach- 
walls, embankments, and wasteway 

Lock No. 4, including excavation 

Section from lock No. 4 to San Juan River, including 
approach- wall and embankments .:....•... 

Conchuda dam, including sluices and machinery. . . . 

Auxiliary wasteway, including sluices, machinery, and 
approach-channels 

San Juan River section 

Lake Nicaragua section 

Lake Nicaragua to lock No. 5, including approach-wall 
to lock and receiving-basins for the Rio Grande and 
Chocolata 

Diversion of the Las Lajas 

Lock No. 5, including excavation 

Dam near Buen Retire 

Section from lock No. 5 to lock No. 6, including approach 
walls and wasteway 

Lock No. 6, including excavation 

Section from lock No. 6 to lock No. 7 , including approach- 
walls, embankments, and wasteway 

Diversion of Rio Grande , 

Lock No. 7, inckiding excavation 

Section from lock No. 7 to lock No. 8, including approach- 
walls, embankments, and wasteway , 

Diversion of Rio Grande , 

Lock No. 8, including excavation , 

Section from lock No. 8 to Brito harbor, including 
approach-wall 

Brito harbor and entrance, including jetty. 

Railroad, including branch line to Conchuda dam site, 
at $75,000 per mile 

Engineering, police, sanitation, and general contingen 
cies, 20 per cent 



Aggregate 



2.15 
7-44 



10 .96 
.20 

16.7s 
.20 

2.77 
.20 

5-30 



49.64 
70-51 



9.09 
. 20 



2 .04 
.20 

1.83 



. 20 
2.43 



.20 

■23 
.92 



18-, .66 



'$2,198,860 



40,100 

116,760 

5.719,689 

6,296,632 
4,050,270 

19-330,654 
3,832,745 

4,310,580 
5,655,871 

8,579,431 
4,017,650 

2,045,322 

23,155,670 

7,877,611 



19,566,575 

199,382 

4,913,512 

125,591 

3,259,283 
4,368,667 

2,309,710 

176,180 

4,709,502 

1,787,496 

117,580 

4,920,899 

553,476 
1,509,470 

7,575,000 

31,644,010 

$189,864,062 



PART VI. 

THE PANAMA ROUTE FOR A SHIP-CANAL 



349. The First Panama Transit Line. — The Panama route as 
aline of transit across the isthmus was established, as near as can 
be determined, between 15 17 and 1520. The first settlement, 
at the site of the town of old Panama, 6 or 7 miles easterly of the 
present city of that name, was begun in August, 151 7. This 
was the Pacific end of the line. The Atlantic end was finally 
established in 15 19 at N ombre de Dios, the more easterly port 
of Ada, where Balboa was tried and executed, having first been 
selected but subsequently rejected. 

The old town of Panama was made a city by royal decree 
from the throne of Spain in September, 1 5 2 1 . At the same time 
it was given a coat of arms and special privileges were conferred 
upon it. The course of travel then established ran by a road 
well known at the present time through a small place called 
Cruces on the river Chagres, about 17 miles distant from Panama. 
It must have been an excellent road for those days. Bridges 
were even laid across streams and the surface was paved, although 
probably rather crudely. According to some accounts it was 
only wide enough for use by beasts of burden, but some have 
stated that it was wide enough to enable two carts to pass each 
other. 

350. Harbor of Porto Bello Established in 1597. — The harbor 
of the Atlantic terminus at Nombre de Dios did not prove entirely 
satisfactory, and Porto Bello, westerly of the former point, was 
made the Atlantic port in 1597 for this isthmian line of transit. 
The harbor of Porto Bello is excellent, and the location was miore 

429 



430 



THE PANAMA ROUTE FOR A SHIP-CANAL. 







S ^ 



IMPORTANCE OF THE ISTHMIAN COMMERCE. 431 

healthful, although Porto Bello itself was subsequently aban- 
doned, largely on account of its unhealthfulness. 

351. First Traffic along the Chagres River, and the Importance 
of the Isthmian Commerce. — As early as 1534, or soon after that 
date, boats began to pass up and down the Chagres River between 
Cruces and its mouth on the Caribbean shore, and thence along 
the coast to Nombre de Dios and subsequently to Porto Bello. 
The importance of the commerce which sprang up across the 
isthmus and in connection with this isthmian route is well set 
forth in the last paragraph on page 28 of the report ot the Isthmian 
Canal Commission : 

' ' The commerce of the isthmus increased during the century 
and Panama became a place of great mercantile importance, with 
a profitable trade extending to the Spice Islands and the Asiatic 
coast. It was at the height of its prosperity in 1585, and was 
called with good reason the toll-gate between western Europe 
and eastern Asia. Meanwhile the commerce whose tolls only 
brought such benefits to Panama enriched Spain, and her people 
were generously rewarded for the aid given by Ferdinand and 
Isabella in the effort to open a direct route westward to Cathay, 
notwithstanding the disadvantages of the isthmian transit." 

352. First Survey for Isthmian Canal Ordered in 1520. — This 
commercial prosperity suggested to those interested in it, and 
soon after its beginning, the possibility of a ship -canal to connect 
the waters of the two oceans. It is stated even that Charles V. 
directed that a survey should be made for the purpose of deter- 
mining the feasibility of such a work as early as 1520. "The 
governor, Pascual Andagoya, reported that such a work was 
impracticable and that no king, however powerful he might be, 
was capable of forming a junction of the two seas or of furnishing 
the means of carrying out such an undertaking." 

353. Old Panama Sacked by Morgan and the Present City 
Founded. — From that time on the city of Panama increased in 
wealth and population in consequence of its commercial impor- 
tance. Trade was established with the west coast of South 
America and with the ports on the Pacific coast of Central Amer- 
ica. In spite of the fact that it was made by the Spaniards a 
fortress second in strength in America only to old Cartagena, it 



432 



THE PANAMA ROUTE FOR A SHIP-CANAL. 



was sacked and burned by Morgan's buccaneers in February, 
167 1. The new city, that is the present city, was founded in 
1673, it not being considered advisable to rebuild on the old site. 




View of the Harbor of Colon. 

354. The Beginnings of the French Enterprise. — The project 
of a canal on this route was kept alive for more than three cen- 
turies by agitation sometimes active and sometimes apparently 
dying out for long periods, until there was organized in Paris, in 
1876, a company entitled ' ' Societe Civile Internationale du Canal 
Tnteroceanique," with Gen. Etienne Turr as president, for the 
purpose of making surveys and explorations for a ship-canal 
between the two oceans on this route. 

355. The Wyse Concession and International Congress of 1879. 
— ^The work on the isthmus for this company was prosecuted 
under the direction of Lieut. L. N. B. Wyse, a French naval 
officer, and he obtained for his company in 1878 a concession 
from the Colombian Government, conferring the requisite rights 



PLAN WITHOUT LOCKS. 433 

and privileges for the construction of a ship-canal on the Panama 
route and the authority to do such other things as might be 
necessary or advisable in connection with that project. This 
concession is ordinarily known as the Wyse concession. 

A general plan for this transisthmian canal was the subject 
of consideration at an international scientific congress convened 
in Paris in May, 1879, and composed of 135 delegates from France, 
Germany, Great Britain, the United States, and other countries, 
but the majority of whom were French. This congress was 
convened under the auspices of Ferdinand de Lesseps, and after 
remaining in session for two weeks a decision, not unanimous, 
was reached that an international canal ought to be located on 
the Panama route, and that it should be a sea-level canal without 
locks. The fact was apparently overlooked that the range be- 
tween high and low tides in the Bay of Panama, about 20 feet, 
was so great as to require a tidal lock at that tei^minus. 

356. The Plan without Locks of the Old Panama Canal Com- 
pany. — A company entitled ' ' Compagnie Universelle du Canal 
Interoceanique " was organized, with Ferdinand de Lesseps as 
president, immediately after the adjournment of the interna- 
tional congress. The purpose of this company was the construc- 
tion and operation of the canal, and it purchased the Wyse con- 
cession from the original company for the sum of 10,000,000 
francs. An immediate but unsuccessful attempt was mads to 
finance the company in August, 1879. This necessitated a second 
attempt, which was made in December, 1880, with success, as 
the entire issue of 600, coo shares of 500 francs each was sold. 
Two years were then devoted to examinations and surveys and 
preliminary work upon the canal, but it was 1883 before operations 
upon a large scale were begun. The plan adopted and followed 
by this company was that of a sea-level canal, affording a depth 
of 29.5 feet and a bottom width of 72 feet. It was estimated 
that the necessary excavation would amount to 157,000,000 cubic 
yards. 

The iVtlantic terminus of this canal route was located at Colon, 
and at Panama on the Pacific side. The line passed through the 
low grounds just north of Monkey Hill to Gatun, 6 miles from the 
Atlantic terminus, and wheve it first met the Chagres River. 



434 



THE PANAMA ROUTE FOR A SHIP-CANAL. 



For a distance of 2 1 miles it followed the general course of the 
Chagres to Obispo, but left it at the latter point and passing up 
the valley of a small tributary cut through the continental divide 
at Culebra, and descended thence by the valley of the Rio Grande 
to the mouth of that river where it enters Panama Bay. The 
total length of this line from 30 feet depth in the Atlantic to the 




Old Dredges near Colon. 

sarne depth in the Pacific was about 47 miles. The maximum 
height of the continental divide on the centre line of the canal in 
the Culebra cut was about 333 feet above the sea, which is a little 
higher than the lowest point of the divide in that vicinity. Im- 
portant considerations in connection with the adjacent align- 
ment made it advisable to cut the divide at a point not its lowest. 
357. The Control of the Floods in the Chagres. — Various 
schemes were proposed for the purpose of controlling the floods 
of the Chagres River, the suddenness and magnitude of which 
were at once recognized as among the greatest difficulties to be 
encountered in the construction of the work. Although it was 
seriously proposed at one time to control this difficulty by building 
a dam across the Chagres at Gamboa,that plan was never adopted, 
and the problem of control of the Chagres floods remained un- 
solved for a long period. 



ESTIMATE OF TIME AND COST. 435 

358. Estimate of Time and Cost —Appointment of Liquidators. 

— It was estimated by de Lesseps in 1880 that eight years would 
be required for the completion of the canal, and that its cost 
would be $127,600,000. The company prosecuted its work with 
activity until the latter part of 1887, when it became evident that 
the sea-level plan of canal was not feasible with the resources 
at its command. Changes were soon made in the plans, and it 
was concluded to expedite the completion of the canal by the 
introduction of locks, deferring the change to a sea-level canal 
until some period when conditions would be sufficiently favorable 
to enable the company to attain that end. Work was prose- 
cuted under this modified plan until 1889, when the company 
became bankrupt and was dissolved by judgment of the French 
court called the Tribunal Civil de la Seine, on February 4, 1889. 
An officer, called the liquidator, corresponding quite closely to a 
receiver in this country, was appointed by the court to take 
charge of the company's affairs. At no time was the project 
of completing the canal abandoned, but the liquidator gradually 
curtailed operations and finally suspended the work on May 15, 
1889. 

359. The " Commission d'Etude." — He determined to take 
into careful consideration the feasibility of the project, and to 
that end appointed a ' ' commission d' etudes," composed of eleven 
French and foreign engineers, headed by Inspector-General 
Guillemain, director of the Ecole Nationale des Pouts et Chausse'es. 
This commission visited the isthmus and made a careful study 
of the entire enterprise, and subsequently submitted a plan for 
the canal involving locks. The cost of completing the entire 
work was estimated to be $1 12,500,000, but the sum of $62, 100,000 
more was added to cover administration and financing, making 
a total of $174,600,000. This commission also gave an approxi- 
mate estimate of the value of the work done and of the plant at 
$87,300,000, to which some have attached much more impor- 
tance than did the commission itself. The latter appears simply 
to have made the ' * estimate" one half of the total cost of com- 
pleting the work added to that of financing and administration, 
as a loose approximation, calling it an "intuitive estimate"; in 
other words, it was simply a guess based upon such information 



436 



THE PANAMA ROUTE FOR A SHIP-CANAL. 



as had been gained in connection with the work done on the 
isthmus. 

360. Extensions of Time for Completion. — By this time the 
period specified for completion under the original Wyse concession 
had nearly expired. The liquidator then sought from the Colom- 
bian Government an extension of ten years, which was granted 
under the Colombian law dated December 26, 1890. This ex- 
tension was based upon the provision that a new company should 
be formed and work on the canal resumed not later than Feb- 




The Partially Completed Panama Canal, about eight miles from Colon. 

ruary 28, 1893. The latter condition was not fulfilled, and a 
second extension was obtained on April 4, 1893, which provided 
that the ten-year extension of time granted in 1890 might begin 
to run at any time prior to October 31, 1894, but not later than 
that date. When it became apparent that the provisions of 



ORGANIZATION OF THE NEW PANAMA CANAL COMPANY. 437 

this last extension would not be carried out an agreement between 
the Colombian Government and the new Panama Company was 
entered into on April 26, 1900, which extended the time of com- 
pletion to October 31, 19 10. The validity of this last extension 
of time has been questioned. 

361. Organization of the New Panama Canal Company, 1894. 
— A new company, commonly known as the new Panama Canal 
Company, was organized on the 20th of October, 1894, with a 
capital stock of 650,000 shares of 100 francs each. Under the 
provisions of the agreement of December 26, 1890, authorizing 
an extension of time for the cons ruction of the canal, 50,000 
shares passed as full-paid stock to the Colombian Government, 
leaving the actual working capital of the new Panama Company 
at 60,000 000 francs, that amount having been subscribed in cash. 
The most of this capital stock was subscribed for by certain 
loan associations, administrator , contractors, and others against 
whom suits had been brought in consequence o the financial 
difficulties of the old company, it having been charged in the 
scandals attending bankruptcy proceedings that they had 
profited illegally. Those suits were discontinued under agree- 
ments to subscribe by the parties interested to the capital stock 
of the new company. The sums thus obtained constituted more 
than two thirds of the 60,000,000 francs remaining of the share 
capital of the new company after the Colombian Government 
received its 50,000 shares. The old company had raised by 
the sale of stock and bond not far from $246,000,000, and the 
number of persons holding the securities thus sold has been 
estimated at over 200,000. 

362. Priority of the Panama Railroad Concession, — The Pan- 
ama Railroad Company holds a concession from the Colombian 
Government giving it rights prior to those of the Wyse con- 
cession, so that the latter could not become effective without the 
concurrence of the Panama Railroad Company. This is shown 
by the language of Article III of the Wyse concession, which, 
reads as follows: 

" If the line of the canal to be constructed from sea to sea 
should pass to the west and to the north of the imaginary straight 
line which -ioins Cape Tiburon with Garachine Point, the grantees 



438 THE PANAMA ROUTE FOR A SHIP-CANAL. 

must enter into some amicable arrangement with the Panama 
Railroad Company or pay an indemnity, which shall be estab- 
lished in accordance with the provisions of Law 46 of August 16, 
1867, ' approving the contract celebration on July 5, 1867, reform- 
atory of the contract of April 15, 1850, for the construction of 
an iron railroad from one ocean to the other through the Isthmus 
of Panama.' " It became necessary, therefore, in order to control 
this feature of the situation, for the old Panama Company to 
secure at least a majority of the stock of the Panama Railroad 
Company. As a matter of fact the old Panama Canal Company 
purchased nearly 69,000 out of the 70,000 sha es of the Panama 
Railroad Company, each such share having a par value of $100. 
These shares of Panama railroad stock are now held in trust 
for the benefit of the new Panama Canal Company. A part of 
the expenditures of the old company therefore covered the cost 
of the Panama Railroad Company's shares, now held in trust for 
the benefit of the new company. 

363. Resumption of Work by the New Company — The Engi- 
neering Commission and the Comite Technique. — Immediately 
after its organization the new Panama Canal Company resumed 
the work of excavation in the Emperador and Culebra cuts with 
a force of men which has been reported as varying between 1900 
and 3600. It also gave thorough consideration to the subject 
of the best plan for the completion of the canal. The company 's 
charter provided for the appointment of a special engineering 
commission of five members by the company and the liquidator to 
report upon the work done and the conclusions to be drawn from 
its study. This report was to be rendered when the amount ex- 
pended by the new company should reach about one half of its 
capital. At the same time the company also appointed a ' ' Comite 
Technique," constituted of fourteen eminent European and 
American engineers, to make a study of the entire project, which 
was to avail itself of existing data and the results of such other 
additional surveys and examinations as it might consider neces- 
sary. The report rendered by this committee was elaborate, 
and it was made November 16, 1898. It was referred to the 
statutory commission of five to which reference has already 
been made, which commission reported in 1899 that the canal 



PLAN OF THE NEW COMPANY. 439 

could be constructed within the Hmits of time and money esti- 
mated. On December 30, 1899, a special meeting of the stock- 
holders of the new company was called, but the liquidator, who 
was one of the largest stockholders, declined to take part in it, 




The Excavation at the Bohio Lock Site. 

and the report consequently has not received the required statu- 
tory consideration. 

364. Plan of the New Company. — The plan adopted by the 
company placed the minimum elevation of the summit level of 
the canal at 97^ feet above the sea, and a maximum at 102^^ feet 
above the same datum. It provided for a depth of 29^- feet of 
water and a bottom width of canal prism of about 98 feet, except 
at special places where this width was increased. A dam was 
to be built near Bohio, which would thus form an artificial lake 
with its surface varying from 52.5 to 65.6 feet above the sea. 
Under this plan there would be a flight of two locks at Bohio, 



440 THE PANAMA ROUTE FOR A SHIP-CANAL. 

about 1 6 miles from the Atlantic end of the canal, and another 
flight of two locks at Obispo about 14 miles from Bohio, thus 
reaching the summit level, a single lock at Paraiso, between 6 
and 7 miles from Obispo, a flight of two locks at Pedro Miguel 
about 1.25 miles from Paraiso, and finally a single lock at Mira- 
flores, a mile and a quarter from Pedro Miguel, bringing the 
canal down to the ocean elevation. The location of this line 
was practically the same as that of the old company. The avail- 
able length of each lock-chamber was 738 feet, while the available 
width was 82 feet, the depth in the clear being 32 feet 10 inches. 
The lifts were to vary from 26 to 33 feet. It was estimated that 
the cost of finishing the canal on this plan would be $101,850,000, 
exclusive of administration and financing. 

In order to control the floods of the Chagres River, and to 
furnish a supply of water for the summit level of the canal, a 
dam was planned to be built at a point called Alhajuela, about 
12 miles from Obispo, from which a feeder about 10 miles long, 
partly an open canal and partly in tunnels or pipe, would conduct 
the water from the reservoir thus formed to the summit level. 

365. Alternative Plan of the New Panama Canal Company. — 
Although the plan as described was adopted, the ' ' Comite Tech- 
nique" apparently favored a modification by which a much 
deeper excavation through Culebra Hill would be made, thus 
omitting the locks at both Obispo and Paraiso, and making the 
level of the artificial Lake Bohio the summit level of the canal. In 
this modified plan the bottom of the summit level would be about 
32 feet above the sea, and the minimum elevation of the summit 
level 61.5 feet above the sea. This modification of plan had the 
material advantage of eliminating both the Obispo and Paraiso 
locks. The total estimated cost of completing the canal under 
this plan was about $105,500,000. Although the Alhajuela 
feeder would be omitted, the Alhajuela reservoir would be re- 
tained as an agent for controlling the Chagres floods and to form 
a reserve water-supply. The difference in cost of these two 
plans was comparatively small, but the additional time required 
to complete that with the lower summit level was probably one 
of the main considerations in its rejection by the committee 
having it under consideration. 



THE ISTHMIAN CANAL COMMISSION AND ITS WORK. 441 

366. The Isthmian Canal Commission and its Work. — This 
brings the project up to the time when the Isthmian Canal Com- 
mission was created in 1899 and when the forces of the new 
Panama Canal Company were employed either in taking care of 
the enormous amount of plant bequeathed to it by the old com- 
pany or in the great excavation at Emperador and Culebra. The 
total excavation of all classes, made up to the time when that 
commission rendered its report, amounted to about 77,000,000 
cubic yards. 

The work of the commission consisted of a comprehensive 
and detailed examination of the entire project and all its acces- 
sories, as contemplated by the new Panama Canal Company, and 
any modifications of its plans, eithe as to alignment, elevations, 
or subsidiary works, which it might determine advisable to 
recommend. In the execution of this work it was necessary, 
among other things, to send engineering parties on the line of the 
Panama route for the purpose of making surveys and exam- 
inations necessary to confirm estimates of the new Panama 
Canal Company as to quantities, elevations, or other physical 
features of the line selected, or required in modifications of 
alignment or plans. In order to accomplish this portion of its 
work the commission placed five working parties on the Panama 
route with twenty engineers and other assistants and forty-one 
laborers. 

367. The Route of the Isthmian Canal Commission that of the 
New Panama Canal Company. — The commission adopted for the 
purposes of its plans and estimates the route selected by the new 
Panama Canal Company, which is essentially that of the old 
company. Starting from the 6 -fathom contour in the harbor of 
Colon, the line follows the low marshy ground adjoining the Bay 
of Limon to its intersection with the Mindi River ; thence through 
the low ground continuing to Gatun, about 6 miles from Colon, 
where it first meets the Chagres River. From this point to 
Obispo the canal line follows practically the general course of 
the Chagres River, although at one point in the marshes below 
Bohio it is nearly 2 miles from the farthest bend in the river, at 
a sm.all place called Ahorca Lagarto. Bohio is about 17 miles 
from the Atlantic terminus, and Obispo about 30 miles. At the 



442 THE PANAMA ROUTE FOR A SHIP-CANAL. 

latter point the course of the Chagres River, passing up-stream, 
lies to the northeast, while the general direction of the canal line 
is southeast toward Panama, the latter leaving the former at this 
location. The canal route follows up the general course of a 
small stream called the Camacho for a distance of nearly 5 miles 
where the continental divide is found, and in which the great 




The French Location for the Bohio Dam. 



Culebra cut is located, about 36 miles from Colon and 13 miles 
from the Panama terminus. After passing through the Culebra 
cut the canal route follows the course of the Rio Grande River 
to its mouth at Panama Bay. The mouth of the Rio Grande, 
where the canal line is located, is about a mile and a half westerly 



PLAN FOR A SEA-LEVEL CANAL. 443 

of the city of Panama. The Rio Grande is a small, sluggish 
stream throughout the last 6 miles of its course, and for that 
distance the canal excavation would be made mostly in soft silt 
or mud. 

Although the line selected by the French company is that 
adopted by the Isthmian Canal Company for its purposes, a num- 
ber of most important features of the general plan have been 
materially modified by the commission, as will be easily under- 
stood from what has already been stated in connection with the 
French plans. 

368. Plan for a Sea-level Canal. — The feasibility of a sea-level 
canal, but with a tidal lock at the Panama end, was carefully con- 
sidered by the commission, and an approximate estimate of the 
cost of completing the work on that plan was made. In round 
numbers this estimated cost was about $250,000,000, and the 
time required to complete the work would probably be nearly 
or quite twice that needed for the construction of a canal with 

'locks. The commission therefore adopted a project for the canal 
with locks. Both plans and estimates were carefully developed 
in accordance therewith. 

369. Colon Harbor and Canal Entrance. — The harbor of Colon 
has been fairly satisfactory for the commerce of that port, but it 
is open to the north, and there are probably two or three days in 
every year during_ which northers blow into the harbor with such 
intensity that ships anchored there must put to 'sea in order to 
escape damage. The western limit of this harbor is an artificial 
point of land formed by material deposited by the old Panama 
Canal Company; it is called Christoph Colon, and near its 
extreme end are two large frame residences built for de Lesseps. 
The entrance to the canal is immediately south of this artificial 
point. The commission projected a canal entrance from the 6- 
fathom contour in the Bay of Limon, in which the harbor of Colon 
is found, swinging on a gentle curve, 6560 feet radius, to the left 
around behind the artificial point just mentioned and then across 
the shore line to the right into the lowland southerly of Colon. 
This channel has a width of 500 feet at the bottom, with side 
slopes of I on 3, except on the second curve, which is somewhat 
sharper than the first, where the bottom width is made 800 feet 



444 THE PANAMA ROUTE FOR A SHIP-CANAL. 

for a length of 800 feet for the purpose of a turning-basin. This 
brings the line into the canal proper, forming a well-protected 
harbor for nearly a mile inside of the shore line. The distance 
from the 6-fathom line to this interior harbor is about 2 miles. 
The total cost of constructing the channel into the harbor and 
the harbor itself is $8,057,707, and the annual cost of mainte- 
nance is placed at $30,000. The harbor would be perfectly 
protected from the northers which occasionally blow with such 
intensity in the Bay of Limon, and it could readily be made in 
all weathers by vessels seeking it. 

370. Panama Harbor and Entrance to Canal. — The harbor at 
the Pacific end of the channel where it joins Panama Bay is of an 
entirely different character in some respects. The Bay of Pan- 
ama is a place of light winds. Indeed it has been asserted that 
the difficulties sometimes experienced by sailing-vessels in finding 
wind enough to take them out of Panama Bay are so serious as 
to constitute a material objection to the location for a ship-canal 
on the Panama route. This difficulty undoubtedly exists at 
times, but the simple fact is to be remembered that Panama was 
a port for sailing-ships for more than two hundred years before a 
steamship was known. The harbor of Panama, as it now exists, 
is a large area of water at the extreme northern limit of the bay, 
immediately adjacent to the city of Panama, protected from the 
south by the three islands of Perico, Naos, and Culebra. It has 
been called a roadstead. There is good anchorage for heavy- 
draft ships, but for the most part the water is shallow. With the 
commission's requirement of a minimum depth of water of 35 
feet, a channel about 4 miles long from the mouth of the Rio 
Grande to the 6-fathom line in Panama Bay must be excavated. 
This channel would have a bottom width of 200 feet with side 
slopes of I on 3 where the material is soft. Considerable rock 
would have to be excavated in this channel. At 4.41 miles from 
the 6-fathom line is located a wharf at the point called La Boca. 
A branch of the Panama Railroad Company runs to this wharf, 
and at the present time deep-draft ships lie up alongside of it 
to take on and discharge cargo. The wharf is a steel frame 
structure, founded upon steel cylinders, carried down to bed-rock 
by the pneumatic process. Its cost was about $1,284,000. The 



THE ROUTE FROM COLON TO BOH 10. 



445 



total cost of the excavated channel leading from Panama harbor 
to the pier at La Boca is estimated by the commission at $1,464,- 




Fig. 1 

LOCATION OF DAM 

SCALE OF FEET 

500 

SCALE OF METERS 



The Boliio Dam Site. 

513. As the harbor at Panama is considered an open roadstead, 
it requires no estimate for annual cost of maintenance. 

371. The Route from Colon to Bohio. — Starting from the har- 
bor of Colon, the prism of the canal is excavated through the low 
and for the most part marshy ground to the little village called 
Bohio. The prism would cut the Chagres River at a number of 
points, and would require a diversion-channel for that river for 
a, distance of about 5 miles on the westerly side of the canal. 
Levees, or protective embankments, would also be required on 
the same side of the canal between Bohio and Gatim, the Chagres 
River leaving the canal line at the latter point on its way to the 
sea. 



446 THE PANAMA ROUTE FOR A SHIP-CANAL. 

372. The Bohio Dam. — The principal engineering feature of 
the entire route is found at Bohio ; it is the great dam across the 
Chagres River at that point, forming Lake Bohio, the summit 
level of the canal. The new Panama Canal Company located this 
dam at a point about 1 7 miles from Colon, and designed to make 
it an earth structure suitably paved on its faces, but without any 
other masonry feature. Some borings had been made along the 
site, and test-pits were also dug by the French engineers. It 
was the conviction of the Isthmian Canal Commission, however, 
that the character of the proposed dam might be affected by a 
further examination of the subsurface material at the site. 
Consequently the boring parties of the Commission sunk a large 
number of bore-holes at six different sections or possible sites 
along the river in the vicinity of the French location. These bor- 
ings revealed great irregularity in the character and disposition 
of the material below the bed and banks of the river. In some 
places the upper stratum of material was almost clear clay, and 
in other places clear sand, while all degrees of admixture of clay 
and sand were also found. At the French site the bed-rock 
at the deepest point is 143 feet below sea-level, with large 
masses of pervious and semi-pervious sand, gravel, and mixtures 
of those materials with clay. Apparently there is a geological 
valley in the rock along the general course of the Chagres River 
in this vicinity filled with sand, gravel, and clay, irregularly dis- 
tributed and with all degrees of admixture, large masses in all 
cases being of open texture and pervious to water. The site 
adopted by the commission for the purposes of its plans and esti- 
mates is located nearly half a mile down the course of the river 
from that selected by the new Panama Canal Company. The 
geological valley is nearly 2000 feet wide at this location, but the 
deepest rock disclosed by the borings of the commission is but 
128 feet below sea-level. The actual channel of the river is not 
more than 150 feet wide and lies on the extreme easterly side of 
the valley. The easterly or right bank of the river at this place 
is clean rock and rises abruptly to an elevation of about 40 feet 
above the river surface at ordinary stages. The left or westerly 
bank of the river is compacted clay and sand, and rises equally as 
abruptly as the rocky bank of the other side, and to about the 



TlIK BO If 10 DAM. 



447 



same elevation. From the top of the abrupt sandy clay bank a 
plateau of rather remarkable uniformity of elevation extends 
for about 1200 feet in a southwesterly direction to the rocky hill in 
which the Bohio locks would be located. The rock slope on the 
easterly or northerly bank of the river runs down under the 
sandy river-bed, but at such an inclination that within the limits 
of the channel the deepest rock is less than 100 feet below sea- 
level. 




Liulc Clay 
tiiind aad Blue Clay 
Oruve) Crusts with 
Sand Seams 



SCALE OF FEET 



60 .100 200 300 
- -X ^Pneumatic Caisson Work 1314 '- ^-4<- -Coffer Dam Work 246- -J<- 




'~'''3x/l^/<'y>////jV//^//'>/V/^^4!^^ 





Yellow CUy and Sand 
Blue Clay and Sand 
Son Ruck. 



Yellow Clay and Sand 

Fine Ura^el 
I Blue CUy aud Sand 
I Sand with Little 
1 Blue Clay 

Blue Clay with 



(Yellow Clay and Sand 
Sand and Yellow Clay 
Sand and Blue Clay 
Blue Clay aud 
Fine Sand 
Soft Bock, 



) Blue Clay 

with Little 
I Blue Clay 

L'lay and Sand 
I Soft Uock 




lake Bohio Full EI.-(-32' ^'st. 
El. +70 
EI.-h40'_V5ji*l 

El +3(1' 



Profile of Bohio Dam Site, selected for 
Plans and Estimate, with section of Dam. 



After the completion of all its examinations and after a care- 
ful study of the data disclosed by them, the commission deemed 



448 THE PANAMA ROUTE FOR A SHIP-CANAL. 

it advisable to plan such a dam as would cut off absolutely all 
possible subsurface flow or seepage through the sand and gravel 
below the river surface. It is to be observed tha such a subsurface 
flow might either disturb the stability of an earth dam or endan- 
ger the water-supply of the summit level of the canal or both. 
The plan of dam finally adopted by the commission for the pur- 
poses of its estimates is shown by the accompanymg plans and 
sections. A heavy core-wall of concrete masonry extends from 
bed-rock across the entire geological valley to the top of the 
structure, or to an elevation of loo feet above sea-level, thus 
absolutely closing the entire valley against any possible flow. 
The thickness of this wall at the bottom is 30 feet, but at an ele- 
vation of 30 feet below sea-level its sides begin to batter at such 
a rate as to make the thickness of the wall 8 feet at its top. On 
either side of this wall are heavy masses of earth embankment 
of selected material properly deposited in layers with surface 
slopes of I on 3 . As shown by the plans, the lower portions of 
the core-wall of this dam would be sunk to bed-rock by the pneu- 
matic process, the joints between the caissons being closed and 
sealed by cylinders sunk in recesses or wells, also as shown by 
the plans. 

373. Variation in Surface Elevation of Lake. — The profile of 
this route shows that the summit level would have an ordinary 
elevation of 85 feet above the sea, but it may be drawn down 
for uses of the canal to a minimum elevation of 82 feet above the 
same datum. On the other hand, under circumstances to be 
discussed later, it may rise during the floods of the Chagres to an 
elevation of 90 or possibly 91 or 92 feet above the level of the sea. 
The top of the dam therefore would be from 8 to 10 feet above 
the highest possible water surface in the lake, which is sufficient 
to guard against wash or overtopping of the dam by waves. 
The total width of the dam at its top would be 20 feet, and the 
entire inner slope would be paved with heavy riprap suitably 
placed and bedded. 

374. Extent of Lake Bohio and the Canal Line in It. — This 
dam would create an artificial lake having a superficial area 
during high water of about 40 square miles. The water would be 
backed up to a point called Alhajuela, about 25 miles up the river 



THE FLOODS OF THE C HAG RES. 



449 



from Bohio. For a distance of nearly 14 miles, i.e., from Bohio 
to Obispo, the route of the canal would lie in this lake. Although 
the water would be from 80 to 90 feet deep at the dam for several 
miles below Obispo, it would be necessary to make some exca- 
vation along the general course of the Chagres in order to 
secure the minimum depth of 3 5 feet for the navigable channel. 
375. The Floods of the Chagres. — The feature of Lake Bohio 
of the greatest importance to the safe and convenient operation 
of the canal is that by which the floods of the river Chagres are 
controlled or regulated. That river is but little less than 150 
miles long, and its drainage area as nearly as can be estimated, 

























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WM 


^^^ 












J 






H 



Location of the Proposed Alhajuela Dam on the Upper Chagres. 



contains about 875 square miles. Above Bohio its current 
moves some sand and a little silt in times of flood, but usuallv 
it is a clear-water stream. In low water its discharge may fall 
to 350 cubic feet per second. 



450 THE PANAMA ROUTE FOR A SHIP-CANAL. 

As is well known, the floods of the Chagres have at times been 
regarded as almost if not quite insurmountable obstacles to the 
construction of a canal on this line. The greatest flood of which 
there is any semblance of a reliable record is one which occurred 
in 1879. No direct measurements were made, but it is stated 
with apparent authority that the flood elevation at Bohio was 
39.3 feet above low water. If the total channel through which 
the flood flowed at that time had been as large as at present, 
actual gaugings or measurements of subsequent floods show that 
the maximum discharge in 1879 might have been at the rate of 
136,000 cubic feet per second. As a matter of fact the total 
channel section in that year was less than it is at the present 
time. Hence if it be assumed that a flood of 140,000 cubic feet 
per second mus be controlled, an error on the safe side will be 
committed. Other great floods of which there are reliable records 
are as follows : 

1885 Height at Bohio 33.8 feet above low water. 
1888: " " " 34.7 " 
1890: " " " 32.1 " 
1893: ". " " 28.5 " 

The maximum measured rate of the 1890 flood was 74,998 
cubic feet per second, and that of 1893, 48,975 cubic feet per 
second. It is clear, therefore, that a flood flow of 75,000 cubic feet 
per second is very rare, and that a flood of 140,000 cubic feet per 
second exceeds that of which we have any record for practically 
forty years. 

376. The Gigante Spillway or Wasteweir. — It is obvious that 
the dam, as designed by the commission, is of such character that 
no water must be permitted to flow over its crest, or even in 
immediate proximity to the down-stream embankment. Indeed 
it is not intended by the commission that there shall be any waste- 
way or discharge anywhere near the dam. At a point about 3 
miles southwest of the site of the dam at Bohio is a low saddle 
or notch in the hills near the head-waters of a small stream called 
the Gigante River. The elevation of this saddle or notch is such 
that a solid miasonry weir with a crest 2000 feet long may readily 



STORAGE IN LAKE BOHIO FOR DRIEST DRY SEASON. 451 

be constructed with its foundations on bed-rock without deep 
excavation. This structure is called the Gigante spillway, and 
all surplus flood-waters from the Chagres would flow over it. 
The waters discharged would flow down to and through some 
large marshes, one called Pena Blanca and another Agua Clara, 
before rejoining the Chagres. Inasmuch as the canal line runs 
just easterly of those marshes, it would be necessary to protect 
it with the levees or embankments to which allusion has already 
been made. These embankments are neither much extended 
nor very costly for such a project. The protection of the canal 
would be further aided by a short artificial channel between the 
two marshes, Pnea Blanca and Agua Clara, for which provision 
is made in the estimates of the commission. After the surplus 
w^aters from the Gigante spillway pass these marshes they again 
enter the Chagres River or flow over the low, half-submerged 
country along its borders, and thence through its mouth to the 
sea near the town of Chagres, about 6 miles northwest of Gatun. 

377. Storage in Lake Bohio for Driest Dry Season. — The ma- 
sonry crest of the Gigante spillway would be placed at an eleva- 
tion of 85 feet above the sea, identically the same as that which 
may be called the normal summit level of the canal. It is esti- 
mated that the total uses of water in the canal added to the loss 
by evaporation, taken at six inches in depth per month, from 
the surface of the lake will amount to about 1070 cubic feet per 
second if the traffic through the canal should amount to 10,000,000 
tons per annum in ships of ordinary size. This draft per second 
is the sum of 406 cubic feet per second for lockage, 207 for evapo- 
ration, 250 for leakage at lock-gates, and 200 for power and other 
purposes, making a total of 1063, which has been taken as 1070 
cubic feet per second. The amount of storage in Lake Bohio 
between the elevations of 85 and 82 feet above sea-level, as 
designed, is sufficient to supply the needs of that traffic in excess 
of the smallest recorded low-water flow of the Chagres River 
during the dry season of a low-rainfall year. The lowest monthly 
average flow of the Chagres on record at Bohio is 600 cubic feet 
per second for March, 1891, and for the purposes of this compu- 
tation that minimum flow has been supposed to continue for 
three months. This includes a sensible margin of safety. In not 



452 



THE PANAMA ROUTE FOR A SHIP-CANAL. 



even the driest year, therefore, can it be reasonably expected 
that the summit level of the canal would fall below the elevation 
of 82 feet imtil the total traffic of the canal carried in ships of 
the present ordinary size shall exceed 10,000,000 tons. If the 
average size of ships continues to increase, as will probably be 
the case, less water in proportion to tonnage will be required for 
the purposes of lockage. This follows from the fact that with a 
given tonnage the greater the capacity of the ships the less the 
number required, and consequently the less will be the number 
of lockages made. 

378. Lake Bohio as a Flood-controller. — On the other hand 
it can be shown that with a depth of 5 feet of water on the crest 
of the Gigante spillway the discharge of that weir 2000 feet long 




The Eastern Face of the Culebra Cut. 

will be at the rate of 78,260 cubic feet per second. If the flood- 
v^aters of the Chagres should flow into Lake Bohio until the head 
of water on the crest of the Gigante weir rises to 7^ feet, the rate 



EFFECT OF HIGHEST FLOODS. 453 

of discharge over that weir would be 140,000 cubic feet per 
second, wliich, as already shown, exceeds at least by a little the 
highest flood-rate on record. The operation of Lake Bohio as 
a flood controller or regulator is therefore exceedingly simple. 
The flood-waters of the Chagres would pour into the lake and 
immediately begin to flow over the Gigante weir, and continue 
to do so at an increasing rate as the flood continues. The dis- 
charge of the weir is augmented by the increasing flood, and 
decreases only after the passage of the crest of the flood-wave. 
No flood even as great as the greatest supposable flood on record 
can increase the elevation of the lake more than 92 to 92!- feet 
above sea-level, and it will only be at long intervals of time when 
floods will raise that elevation more than about 90 feet above 
sea-level. The control is automatic and unfailingly certain. 
It prevents absolutely any damage from the highest supposable 
floods of the Chagres, and reserves in Lake Bohio all that is re- 
quired for the purposes of the canal and for wastage by evapora- 
tion through the lowest rainfall season. The floods of the Chagres, 
therefore, instead of constituting the obstacle to construction 
and convenient maintenance of the canal heretofore supposed, 
are deprived of all their prejudicial effects and transformed into 
beneficial agents for the operation of the waterway. 

379. Effect of Highest Floods on Current in Channel in Lake 
Bohio. — The highest floods are of short duration, and it can be 
stated as a general law that the higher the flood the shorter its 
duration. The great floods which it is necessary to consider in 
connection with the maintenance and operation of this canal 
would last but a comparatively few hours only. The great flood- 
flow of 140,000 cubic feet per second would increase the current 
in the narrowest part of the canal below Obispo to possibly 5 
feet per second for a few hours only, but that is the only incon- 
venience which would result from such a flood-discharge. That 
velocity could be reduced by additional excavation. 

380. Alhajuela Reservoir not Needed at Opening of Canal. — Inas- 
much as this system of control, devised and adopted by the Isth- 
mian Canal Commission, is completely effective in regulating 
the Chagres floods; the reservoir proposed to be constructed by 
the new Panama Canal Company at Alhajuela on the Chagres 



454 THE PANAMA ROUTE FOR A SHIP-CANAL. 

about 1 1 miles above Obispo is not required, and the cost of its 
construction would be avoided. It could, however, as a project 
be held in reserve. If the traffic of the canal should increase to 
such an extent that more water would be needed for feeding the 
summit level, the dam could be built at Alhajuela so as to impound 
enough additional water to accommodate, with that stored in 
Lake Bohio, at least five times the 10,000,000 annual traffic 
already considered. Its existence would at the same time 
act with substantial effect in controlling the Chagres floods and 
relieve the Gigante spillway of a corresponding amount of duty. 

381. Locks on Panama Route. — The locks on the Panama 
route are designed to have the same dimensions as those in Nica- 
ragua, as was stated in the lecture on that route. The usable 
length is 740 feet and the clear width 84 feet. They would be 
built chiefly of concrete masonry, while the gates would be of 
steel and of the mitre type. 

382. The Bohio Locks. — The great dam at Bohio raises the 
water surface in the canal from sea-level in the Atlantic maritime 
section to an ordinary maximum of 90 feet above sea-level; in 
other words, the maximum ordinary total lift would be 90 feet. 
This total lift is divided into two parts of 45 feet each. 
There is therefore a flight of two locks at Bohio ; indeed there are 
two flights side by side, as the twin arrangement is designed to 
be used at all lock sites on both routes. The typical dimensions 
and arrangements of these locks, with the requisite culverts and 
other features, are shown in the plans and sections between 
pages 396 and 397, Part V. They are not essentially different 
from other great modern ship-canal locks. The excavation for 
the Bohio locks is made in a rocky hill against which the south- 
westerly end of the proposed Bohio dam rests, and they are less 
than 1000 feet from it. 

383. The Pedro Miguel and Miraflores Locks. — After leaving 
Bohio Lake at Obispo a flight of two locks is found at Pedro Miguel, 
about 7.9 miles from the former or 21^ miles from Bohio. These 
locks have a total ordinary maximum lift of 60 feet, divided into 
two lifts of 30 feet each. The fifth and last lock on the route is 
at Miraflores. The average elevation of water between Pedro 
Miguel and Miraflores is 30 feet above mean sea-level. Inas- 



GUARD-GATES NEAR OBISPO. 455 

much as the range of tide between high and low in Panama Bay 
is about 20 feet, the maximum Hft at Miraflorcs is 40 feet and 
the minimum about 20. The twin locks at Miraflores bring the 
canal surface down to the Pacific Ocean level, the distance from 
those locks to the 6-fathom curve in Panama Bay being 8.54 
miles. There are therefore five locks on the Panama route, all 
arranged on the twin plan, and, as on the Nicaragua route, all 
are founded on rock. 

384. Guard-gates near Obispo. — Near Obispo a pair of guard- 
gates are arranged ' ' so that if it should become necessary to 
draw off the water from the summit cut the level of Lake Bohio 
would not be affected." 

385. Character and Stability of the Culebra Cut. — An unpre- 
cedented concentration of heavy cutting is found between Obispo 
and Pedro ]\Iiguel. This is practically one cut, although the 
northwesterly end toward Obispo is called the Emperador, while 
the deepest part at the other end, about 3 miles from Pedro Miguel, 
is the great Culebra cut with a maximum depth on the centre 
line of the canal of 286 ft. On page 93 of the Isthmian 
Canal Commission's report is the following reference to the ma- ^ 

terial in this cut : ' ' There is a little very hard rock at the eastern \ 

end of this section, and the western 2 miles are in ordinary ma- 
terials. The remainder consists of a hard indurated clay, with 
some softer material at the top and some strata and dikes of hard 
rock. In fixing the price it has been rated as soft rock, but it 
must be given si pes equivalent to those in earth. This cut has 
been estimated on the basis of a bottom width of 150 feet, with 
side slopes of i on i.' When the old Panama Canal Company 
began its excavation in this cut considerable difficulty was ex- 
perienced by the slipping of the material outside of the limits of 
the cut into the excavation, and the marks of that action can be 
seen plainly at the present time. This experience has given an 
impression that much of the material in this cut is unstable, but 
that impression is erroneous. The clay which slipped in the 
early days of the work was not drained, and like wet clay in 
numerous places in this country it slipped down into the excava- 
tion. This material is now drained and is perfectly stable. 
There is no reason to anticipate any future difficulty if reasonable 



456 



THE PANAMA ROUTE FOR A SHIP-CANAL. 



conditions of drainage are maintained. The high faces of the 
cut will probably weather to some extent, although experience 
with such clay faces on the isthmus indicates that the amount of 




The Culebra Cut. 

such action will be small. As a matter of fact the material in 
which the Culebra cut is made is stable and will give no sensible 
difficulty in maintenance. 

386. Small Diversion-channels. — Throughout the most of the 
distance between Colon and Bohio on the easterly side of the 
canal the French plan contemplated an excavated channel to 
receive a portion of the waters of the Chagres as well as the flow 
of two smaller rivers, the Gatuncillo and the Mindi, so as to con- 



LENGTH AND CURVATURE. 



457 



duct them into the Bay of Manzanillo, immediately to the east 
of Colon. That so-called diversion-channel was nearly completed. 
Under the plan of the commission it would receive none of the 
Chagres flow, but it would be available for intercepting the drain- 
age of the high ground easterly of the canal line and the flow of 
the two small rivers named, so that these waters would not find 
their way into the canal. There are a few other small works of 
similar character in different portions of the line, all of which 
were recognized and provided for by the commission. 

387. Length and Curvature. — The total length of the Panama 
route from the 6 -fathom curve at Colon to the same curve in 
Panama Bay is 49.09 miles. The general direction of the route 
in passing from Colon to Panama is from northwest to southeast, 
the latter point being about 2 2 miles east of he Atlantic terminus. 
The depression through which the line is laid is one of easy topog- 
raphy except at the continental divide in the Culebra cut. As 
a consequence there is little heavy work of excavation, as such 
matters go except in that cut. A further consequence of such 
topography is a comparatively easy alignment, that is, one in 
which the amount of curvature is not high. The smallest radius 
of curvature is 3281 feet at the entrace to the inner harbor at 
the Colon end of the route, and where the width is 800 feet. The 
radii of the remaining curves range from 6234 feet to 19,629 feet. 

The following table gives all the elements of curvature on the 
route and indicates that it is not excessive : 



Number of Curves. | Length. 


Radius. 


Total Curvature. 


I 

I 

4 

15 

4 

2 


Miles 

0.88 

.48 

4.22 

II .61 

2.44 
I .67 

•73 
.82 


Feet. 

19,629 

13,123 

11,483 

9,842 

8,202 

6,562 

6,234 

3,281 


14 17 

II 04 

III 32 

355 50 
90 20 
77 00 

35 45 
75 51 


I 

I 


22.85 




771 39 



388. Principal Items of Work to be Performed. — The principal 
items of the total amount of work to be performed in completing 



458 



THE PANAMA ROUTE FOR A SHIP-CANAL. 



the Panama Canal, under the plan of the commission, can be 
classified as shown in the following table : 

Dredging 27,659,540 cu. yds. 

Dry earth 14,386,954 

Soft rock 39.893.235 " 

Hard rock 8,806,340 " 

Rock under water 4,891,667 " 

Embankment and back-filling 1,802,753 " 

Total 97,440,489 " 

Concrete 3,762,175 cu. yds. 

Granite 13.820 " 

Iron and steel 65,248,900 lbs. 

Excavation in coffer-dam 7,260 cu. yds. 

Pneumatic work 108,410 " 

389. Lengths of Sections and Elements of Total Cost. — The 

lengths of the various sections of this route and the costs of 
completing the work upon them are fully set forth in the following 
table, taken from the commission's report, as were the two pre- 
ceding : 

TOTAL ESTIMATED COST. 



Miles. 



Cost. 



Colon entrance and harbor 

Harbor to Bohio locks, including levees 

Bohio locks, including excavation .' . . . . 

Lake Bohio 

Obispo gates 

Culelsra section 

Pedro Miguel locks, including excavation and dam. 

Pedro Migviel level 

Miraflores locks, including excavation and spillway 

Pacific level 

Bohio dam • • • 

Gigante spillway 

Pefia Blanca outlet 

Chagres diversion 

Gatun diversion 

Panama Railroad diversion 



2-39 
14.42 

■35 
13.61 



7.91 
•35 

1-33 
. 20 

8.53 



*h, 057, 707 
11,099,839 

11.567,275 

2.952,154 

295.434 

44,414,460 
9,081,321 
1,192,286 
5.781,401 

12,427,971 
6,369,640 
1,209,419 
2,448,076 
1,929,982 
100,000 
1,267,500 



Total. 



49.09 



Engineering, police, sanitation, and general contingen- 
cies, 20 per cent. 



120,194,465 
24,038,893 



Aggregate 



$144,233,358 



The item in this table called Panama Railroad diversion affords 
provision for the reconstruction of the railroad necessitated by 



THE TWENTY PER CENT ALLOWANCES FOR EXIGENCIES. 459 

the formation of Lake Bohio. That lake would submerge the 
present location of the railroad for 14 or 15 miles. 



The Culebra Cut with Steamer Deutschland in it. 

390. The Twenty Per Cent Allowances for Exigencies. — It will 
be observed that in the estimates of cost of the canal on both the 
Nicaragua and the Panama routes, 20 per cent is allowed for 
' ' engineering, police, sanitation, and general contingencies." For 
the purposes of comparison the same percentage to cover these 
items was used on both routes. As a matter of fact the large 
amoimt of work which has already been performed on the Panama 
route removes many uncertainties as to the character of material 
and other features of difficulty which would be disclosed only 
after the beginning of the work in Nicaragua. It has therefore 
been contended with considerable basis of reason that a less 
percentage to cover these uncertainties should be employed in 
connection with the Panama estimates than in connection with 
those for the Nicaragua route. Indeed it might be maintained 
that the exigencies which increase cost should be made propor- 
tional to the length of route and the untried features. On the 
other hand, both Panama and Colon are comparatively large 
centres of population, and, furthermore, there is a considerable 
population stretched along the line of the Panama Railroad be- 
tween those points. The climate and the unsanitary condition 
of practically every centre of population in Central America 
and on the isthmus contribute to the continual presence of tropi- 
cal fevers, and other diseases contingent upon the existing con- 
ditions of life. It is probable, among other things, that yellow 
fever is always present on the isthmus. Inasmuch as the Nica- 
ragua route is practically without population, the amount of 



460 THE PANAMA ROUTE FOR A SHIP-CANAL. 

disease existing along it is exceedingly small, there being 
practically no people to be sick. The initial expenditure for the 
sanitation of the cities at the extremities of the Panama route, 
as well as for the country between, would be far greater for 
that route than on the Nicaragua. This fact compensates, to 
a substantial extent at least, for the physical uncertainties on 
the Nicaragua line. Indeed a careful examination of all the 
conditions existing on both routes indicates the reasonableness 
of applying the same 20 per cent to both total estimates of cost. 

391. Value of Plant, Property, and Rights on the Isthmus. — 
The preceding estimated cost of $144,233,358 for completing the 
Panama Canal must be increased by the amount necessary to be 
paid for all the property and rights of the new Panama Canal 
Company on the isthmus. A large amount of excavation has been 
performed, amounting to 77,000,000 cubic yards of all classes of 
materials, and nearly all the right of way has been purchased. 
The new Panama Canal Company furnished the commission with 
a detailed inventory of its entire properties, which the latter 
classified as follows: 

1. Lands not built on. 

2. Buildings, 2431 in number, divided among 47 subclassifi- 
cations. 

3. Furniture and stable outfit, with 17 subclassifications. 

4. Floating plant and spare parts, with 24 subclassifications. 

5. Rolling plant and spare parts, with 17 subclassifications. 

6. Plant, stationary and semi-stationary, and spare parts, 
with 25 subclassifications. 

7. Small material and spare parts, with 4 subclassifications. 

8. Surgical and medical outfit. 

9. Medical stores. 

10. Office supplies, stationery. 

11. Miscellaneous supplies, with 740 subclassifications. 

The commission did not estimate any value for the vast 
amount of plant along the line of the canal, as its condition in 
relation to actual use is uncertain, and the most of it would not 
be available for efficient and economical execution of the work 
by modem American methods. Again, a considerable amount 



NEW COMPANY'S OFFER TO SELL FOR FORTY MILLIONS. -iOl 

of excavated material along some portions of the line has been 
deposited in spoil-banks immediately adjacent to the excavation 
from which it was taken, and would have to be rehandled in 
forming the increased size of prism contemplated in the com- 
mission's plan. 

In view of all the conditions affecting it, the commission made 
the following elstimate of the value of the property of the new 
Panama Canal Company, as it is now found on the Panama route : 

Canal excavation $21,020,386 

Chagres diversion 178,186 

Gatun diversion 1,396,456 

Railroad diversion (4 miles) 300,000 

22,895,028 
Contingencies, 20 per cent 4,579,005 

Aggregate 27,474,033 

Panama Railroad stock at par 6,850,000 

Maps, drawings, and records 2,000,000 



,324,033 _ 

The commission added 10 per cent to this total "to cover 
omissions, ' making the total valuation of the" property and 
rights as now existing, $40,000,000. 

In computing the value of the channel excavation in the above 
tabulation it was estimated that " the total quantity of excava- 
tion which will be of value in the new plan is 39,586,332 cubic 
yards." 

392. Offer of New Panama Canal Company to Sell for $40,000,000. 
—In January, 1902, the new Panama Canal Company offered to 
sell and transfer to theUnited States Government all its property 
and rights on the isthmus of every description for the estimate 
of the commission, viz., $40,000,000. In order to make a proper 
comparison between the total costs of constructing the canal 
on the two routes it is necessary to add this $40,000,000 to the 
preceding aggregate of $144,233,358, making the total cost of 
the Panama Canal $184,233,358. It will be remembered that 



462 



THE PANAMA ROUTE FOR A SHIP-CANAL. 



the corresponding total cost of the Nicaragua Canal would be 
$189,864,062. 

393. Annual Costs of Operation and Maintenance. — It is ob- 
vious that the cost of operating and maintaining a ship-canal 
across the American isthmus would be an annual charge of large 




The Railroad Pier at La Boca, the Panama end of the Canal. 

amount. A large organized force would be requisite, and no 
small amount of material and work of various kinds and grades 
would be needed to maintain the works in suitable condition. 
The commission made very careful and thorough studies to 
ascertain as nearly as practicable what these comparative costs 
would be. In doing this it gave careful consideration to the 
annual expenditures made in maintaining the various ship-canals 
of the world, including the Suez, Manchester, Kiel, and St. Mary's 



VOLCANOES AND EARTHQUAKES. 463 

Falls canals. The conclusion reached was that the estimated 
annual costs of maintenance and operation could reasonably be 
taken as follows : 

For the Nicaragua Canal $3,300,000 

For the Panama Canal 2,000,000 

Difference in favor of Panama $1,300,000 

394. Volcanoes and Earthquakes. — Much has been written 
regarding the comparative liability to damage of canal works 
along these two routes by volcanic or seismic agencies. As is 
well known, the entire Central American isthmus is a volcanic 
region, and in the past a considerable number of destructive 
volcanic eruptions have taken place at a number of points. 
There is a line of live volancoes extending southeasterly through 
Nicaragua and Costa Rica. Many earthquake shocks have 
occurred throughout Nicaragua, Costa Rica, and the State of 
Panama, some of which have done more or less damage in large 
portions of those districts. At the same time many buildings 
which have been injured have not been substantially built. In 
fact that has generally been the case. Both routes lie in dis- 
tricts that are doubtless subject to earthquake shocks, but there 
is little probability that the substantial structures of a canal along 
either line would be essentially injured by them. The conclu- 
sions of the commission as to this feature of the matter are con- 
cisely stated in three paragraphs at the top of page 170 of its 
report : 

"It is possible and even probable that the more accurately 
fitting portions of the canal, such as the lock-gates, may at times 
be distorted by earthquakes, and some inconvenience may result 
therefrom. That contingency may be classed with the accidental 
collision of ships with the gates, and is to be provided for in the 
same way, by duplicate gates. 

"It is possible also that a fissure might open which would 
drain the canal, and, if it remained open, might destroy it. This 
possibility should not be erected by the fancy into a threatening 
danger. If a timorous imagination is to be the guide, no great 
work can be undertaken anywhere. This risk may be classed 



464 THE PANAMA ROUTE FOR A SHIP-CANAL. 

with that of a great conflagration in a city Hke that of Chicago 
in 1871, or Boston in 1872. 

"It is the opinion of the commission that such danger as 
exists from earthquakes is essentially the same for both the 
Nicaragua and Panama routes, and that in neither case is it 
sufficient to prevent the construction of the canal." 

The Nicaragua route crosses the line of live volcanoes run- 
ning from northwest to southeast through Central America, 
and the crater of Ometepe in Lake Nicaragua is about it 
miles only from the Hne. The eruptions of Pelee and Soufrifere 
show that such proximity of possible volcanic action may be a 
source of great danger, although even the destruction by them 
does not certainly indicate damage either to navigation or to 
canal structures at the distance of 11 miles. Whatever vol- 
canic danger may exist lies on the Nicaragua route, for there 
is no volcano nearer than 175 miles to the Panama route. 

395. Hygienic Conditions on the Two Routes. — The relative 
healthfulness of the two routes has already been touched upon. 
There is undoubtedly at the present time a vast amount of un- 
healthfulness on the Panama route, and practically none on the 
Nicaragua route, but this is accounted for when it is remembered, 
as has also been stated, that there is practically no population 
on the Nicaragua route and a comparatively large population 
along the Panama line. There is a wide-spread, popular impres- 
sion that the Central American countries are necessarily intensely 
unhealthful. This is an error, in spite of the facts that the con- 
struction of the Panama Railroad was attended with an appalling 
amount of sickness and loss of life, and that records of many 
epidemics at other tim^es and in other places exist in nearly all 
of these countries. There are the best of good reasons to believe 
that with the enforcement of sanitary regulations, which are now 
well understood and completely available, the Central American 
countries would be as healthful as our Southern States. A proper 
recognition of hygienic conditions of life suitable to a tropical 
climate would work wonders in Central America in reducing 
the death-rate. At the present time the domestic administra- 
tion of most of the cities and towns of Nicaragua and Panama, 
as well as the generality of Central American cities, is characterized. 



TIME OF PASSAGE TH ROUGH THE CANAL. 465 

by the absence of practically everything which makes for public 
health, and by the presence of nearly every agency working for 
the diseases which flourish in tropical climates. When the United 
States Government reaches the point of actual construction of 
an isthmian canal the sanitary features of that work should be 
administered and enforced in every detail with the rigor of the 
most exacting military discipline. Under such conditions, epi- 
demics could either be avoided or reduced to manageable dimen- 
sions, but not otherwise. The commission concluded that 
' ' Existing conditions indicate hygienic advantages for the Nica- 
ragua route, although it is probable that no less effective sanitary 
measures must be taken during construction in the one case 
than in the other." 

396. Time of Passage through the Canal. — The time required 
for passing through a transisthmian canal is affected by the 
length, by the number of locks, by the number of curves, and by 
the sharpness of curvature. The speed of a ship, and consequently 
the time of passage, is also aft'ected by the depth of water under 
its keel. It is well known that the same power applied to a ship 
'in deep water of unlimited width will produce a much higher rate 
'of movement than the same power applied to the same ship in a 
restricted waterway, especially when the draft of the ship is but 
little less than the depth of water. These considerations have 
important bearings both upon the dimensions of a ship-canal and 
upon the time required to pass through it. They were most care- 
fully considered by the commission, as were also such other mat- 
ters as the delay incurred in passing through the locks on each 
line, the latter including the delay of slowing or approaching the 
lock and of increasing speed after passing it, the time of opening 
and closing the ga'es, and the time of emptying and filling the 
locks. It is also evident that ships of various sizes will require 
different times for their passage. After giving due w^eight to all 
these considerations i'; was found that what may be called an 
average ship would require twelve hours for passing through 
the Panama Canal and thirty-three hours for passing through 
the Nicaragua Canal. Approximately speaking, therefore, it 
may be stated that an average passage through the former water- 
way will require but one third the time needed for the latter. 



466 



THE PANAMA ROUTE FOR A SHIP-CANAL. 



397. Time for Completion on the Two Routes. — The time in 
which an isthmian canal may be completed and ready for traffic 
is an element of the problem of much importance. There are 
two features of the work to be done at Panama, each of which is 
of sufficient magnitude to affect to a controlling extent the time 
required for the construction of the canal, viz., the Bohio dam 
and the Culebra cut. Both of these portions of the work may, 




A Street in Panama. 

however, be prosecuted concurrently and with entire independ- 
ence of each other. There are no such features on the Nicaragua 
route, although the cut through the divide west of the lake is 
probably the largest single work on that route. In considering 
this feature of the matter it is well to observe that the total 
amount of excavation and embankment of all grades on the 
Nicaragua route is practically 228,000,000 cubic yards, while 
that remaining to be done on the Panama route is but little more 
than 97,000,000 cubic yards, or 43 per cent of the former. The 



TIME FOR COMPLETION ON THE TWO ROUTES. 



4G7 



accompanying figures show the relative quantities of total 
excavation, concrete, iron, and steel required in construction 
along the two routes, as well also as the total amounts and radii 
of curvature. 




-•.■'■" 




»°l,' 


■ »■-* 


Concrete 
3,702,175 
Cubic Varda 




t.'f 


'." '.*4 * ^ V*. 


'A' • 



NICARAGUA 




;';-:'':':'V-'-v?- 


»■':; 




Concrete 


.v."'- 


'•'■► 


3,825.101 


"-►. 




Cubic Yards 




:•'•> 


••^:;-:^>;-. 


"'•.♦. 




NUMBER OF CURVES = 29 

LENGTH OF CURVES =22. 85 MILES - 

TOTAL CURVATURE^ 771°39' 



NUMBER OF CURVES =56 
LENGTH OF CURveS^49.29 MILES 
TOTAL CURVATURE =2339°50>b' 



PANAMA = 't9.09 MILES 



NICARAGUA = 183. 66 MILES 



Diagrams comparing some of the main Elements of the two Routes. 

The commission has estimated ten years for the completion of 
the canal on the Panama route and eight years for the Nicaragua 
route, including in both cases the time required for preparation 



468 THE PANAMA ROUTE FOR A SHIP-CANAL. 

and that consumed by unforeseen delays. The writer beheves 
that the actual circumstances attending work on the two routes 
would justify an exchange of these time relations. There is 
great concentration of work in the Culebra-Emperador cut on 
the Panama route, covering about 45 per cent of the total ex- 
cavation of all grades (43,000,000 cubic yards), which is dis- 
tributed over a distance of about 7 miles, with the location of 
greatest intensity at Culebra. This demands efficient organi- 
zation and special plant so administered as to reduce the working 
force to an absolute minimum by the employment of machinery 
to the greatest possible extent. A judicious, effective organiza- 
tion and plant would transform the execution of this work into 
what may be called a manufactory of excavation with all the 
intensity of direction and efficiency of well designed and admin- 
istered machinery which characterizes the concentration of labor 
and mechanical appliances in great manufacturing establish- 
ments. Such a successful installation would involve scarcely 
more advance in contract operations than was exhibited, in its 
day, in the execution of the work on the Chicago Drainage-canal. 
By such means only can the peculiar difficulties attendant upon 
the execution of great works in the tropics be reduced to con- 
trollable dimensions. The same general observations may be 
applied to the construction of the Bohio dam, even should a no 
more favorable site be found. 

The greatest concentration of excavation on the Nicaragua 
route is between the lake and the Pacific, but it constitutes only 
10 per cent of the total excavation of all grades, and it can be 
completed in far less time than the great cut on the Panama 
route. If this were the only great feature of work besides the 
dam, the time for completion of work on this route would be 
materially less than that required for the Panama crossing. As a 
matter of fact, there are a succession of features of equivalent 
magnitude, or very nearly so, from Greytown nearly to Brito, 
extending over a distance of at least 175 miles, requiring the 
construction of a substantial service railroad over a considerable 
portion of the distance prior to the beginning of work. This atten- 
uation of work requires the larger features to be executed in 
succession to a considerable extent, or much duplication of plant 



INDUSTRIAL AND COMMERCIAL VALUE OF THE CANAL. 469 

and the employment of a great force of laborers, practically all 
of whom must be foreigners, housed, organized, and maintained 
in a practically uninhabited tropical country where many serious 
difficulties reach a maximum. It is not within the experience 
of civil engineers to execute by any practicable means that kind 
of a programme on schedule time. The weight of this observation 
is much increased when it is remembered that the total volume 
of work may be taken nearly twice as great in Nicaragua as at 
Panama, and that, large portions between Lake Nicaragua and 
the Caribbean Sea must be executed in a region of continual and 
enormous rainfall. It would seem more reasonable to the writer 
to estimate eight years for the completion of the Panama Canal 
and ten years for the completion of the Nicaragua Canal. 

398. Industrial and Commercial Value of the Canal. — The 
prospective industrial and commercial value of the canal also 
occupied the attention of the commission in a broad and careful 
study of the elements which enter that part of the problem. It 
is difficult if not impossible to predict just what the effect of a 
transisthmian canal would be either upon the ocean commerce 
of the United States or of other parts of the world, but it seems 
reasonable to suppose from the result of the commission's exam- 
inations that had the canal been in existence in 1899 at least 
5,000,000 tons of the actual traffic of that year would have been 
accommodated by it. The opening of such a waterway, like the 
opening of all other traffic routes, induces the creation of new 
traffic to an extent that cannot be estimated, but it would appear 
to be reasonable to suppose that within ten years from the date 
of its opening the vessel tonnage using it would not be less than 
10,000,000 tons. 

The Nicaragua route would favor in distance the traffic be- 
tween our Atlantic (including Gulf) and Pacific ports. The dis- 
tances between our Atlantic ports and San Francisco would be 
about 378 nautical miles less than by Panama. Between New 
Orleans and San Francisco this difference in favor of the route 
by Greytown and Brito would be 580 nautical miles. It must 
be remembered, however, that the greater time by at least twenty- 
four hours required for passage through the Nicaragua Canal 
practically obliterates this advantage, and in some cases would 



470 



THE PANAMA ROUTE FOR A SHIP-CANAL. 




COMPARLSOX OF ROUTES. 471 

throw the advantage in favor of the Panama waterway. This 
last observation would hold with particular force if for any reason 
a vessel should not continue her passage, or should continue it 
at a reduced speed during hours of darkness, which could not be 
escaped on the Nicaragua Canal, but might be avoided at Panama. 
For all traffic between the iVtlantic (including Gulf) ports and the 
west coast of South America the Panama crossing would be the 
most advantageous. As a matter of fact, while there may be 
some small advantage in miles by one route or the other for the 
traffic between some particular points, on the whole neither route 
would have any very great advantage over the other in point of 
distance or time; either would serve efficiently the purposes of 
all ocean traffic in which the ports of the United States are 
directly interested. 

The effect of this ship waterway upon the well-being of the 
United States is not altogether of a commercial character. As 
indicated by the commission, this additional bond between the 
two portions of the country will have a beneficial effect upon the 
unity of the political interests as well as upon the commercial 
welfare of the country. Indeed it is the judgment of many 
well-informed people that the commercial advantages resulting 
from a closer touch betw^een the Atlantic and Pacific coasts of 
the country are of less consequence than the unifying of political 
interests. 

In a final comparison between the two routes it is to be 
remembered that the concession under which the new Panama 
Company has been and is now prosecuting its work is practically 
valueless for the purposes of this country. It will therefore be 
necessary to secure from the republic of Colombia, for the Pan- 
ama route, as well as from the republics of Nicaragua and Costa 
Rica, for the Nicaragua route, such new concessions as may be 
adequate for all the purposes of the United States in the con- 
struction of this transisthmian canal. The cost of those con- 
cessions in either case must be added to the estimated total cost 
of the work, as set forth, in order to reach the total cost of the 
canal along either route : 

39Q. Comparison of Routes. — Concisely stating the situation^ 
its main features may be expressed somewhat as follows: 



472 THE PANAMA ROUTE FOR A SHIP-CANAL. 

Both routes are entirely ' ' practicable and feasible." 

Neither route has any material commercial advantage over 
the other as to time, although the distance between our Atlantic 
(including Gulf) and Pacific ports is less by the Nicaragua route. 

The Panama route has about one fourth the length of that in 
Nicaragua; it has less locks, less elevation of summit level, and 
far less curvature, all contributing to correspondingly decreased 
risks peculiar to the passage through a canal. The estimated 
annual cost of operation and maintenance of the Panama route 
is but six tenths that for the Nicaragua route. 

The harbor features may be made adequate for all the needs 
of a canal by either route, with such little preponderance of 
advantage as may exist in favor of the Panama crossing. 

The commission estimated ten years for the completion of 
the Panama Canal and eight years for the Nicaragua waterway, 
but the writer believes that these relations should be exchanged, 
or at least that the time of completion for the Panama route 
should not be estimated greater than for the Nicaragua. 

The water-supply is practically unlimited on both routes, 
but the controlling or regulating works, being automatic, are 
much simpler and more easily operated and maintained on the 
Panama route. 

The Nicaragua route is practically uninhabited, and conse- 
quently practically no sickness exists there. On the Panama 
route, on the contrary, there is a considerable population extend- 
ing along the entire line, among which yellow fever and other 
tropical diseases are probably always found. Initial sanitary 
works of much larger magnitude would be required, on the Pan- 
ama route than on the Nicaragua, although probably as rigorous 
sanitary measures would be required during the construction of 
the canal on one route as on the other. 

The railroad on the Panama route and other facilities offered 
by a considerable existing population render the beginning of 
work and the housing and organization of the requisite labor 
force less difficult and more prompt than on the Nicaragua route. 

The greater amount of work on the Nicaragua route, and its 
distribution over a far greater length of line, involve the employ- 



COMPARISON OF ROUTES. 4:73 

ment of a correspondingly greater force of laborers, with greater 
attendant difficulties, for an equally prompt completion of the 
work. 

The relative seismic conditions of the two routes cannot be 
quantitatively stated with accuracy, but in neither case are they 
of sufficient gravity to cause anxiety as to the effects upon com- 
pleted canal structures. 

Concessions and treaties require to be secured and negotiated 
for the construction of the canal on either route, and under the 
conditions created by the $40,000,000 offer of the new Panama 
Canal Company this feature of both routes appears to possess 
about the same characteristics, although the Nicaragua route is, 
perhaps, freer from the complicating shadows of prior rights and 
concessions. 



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Part I.— Stresses in Simple Trusses Svo, 2 50 

Part XL— Graphic Statics Svo, 2 50 

Part III. — Bridge Design. Fourth Ed., Rewritten Svo, 2 50 

Part IV.— Higher Structures ; Svo, 2 50 

Morisom's Memphis Bridge 4to, 10 00 

Waddell's De Pontibus, a Pocket Book for Bridge Engineers. 

16mo, mor., 3 00 

" Specifications for Steel Bridges 12mo, 1 25 

Wood's Treatise on the Theory of the Construction of Bridges 

and Roofs Svo, 2 00 

Wright's Designing of Draw-spans: 

Part I. — Plate-girder Draws Svo, 2 50 

Part II. — Riveted-truss and Pin-connected Long-span Draws. 

Svo, 2 50 

Two parts in one volume Svo, 3 50 

HYDRAULICS. 

Bazin's Experiments upon the Contraction of the Liquid Vein 

Issuing from an Orifice. (Trautwine.) Svo, 

Bovey's Treatise on Hydraulics Svo, 

Church's Mechanics of Engineering Svo, 

" Diagrams of Mean Velocity of Water in Open Channels 

paper, 
Coffin's Graphical Solution of Hydraulic Problems. .16mo, mor., 
Flather's Dynamometers, and the Measurement of Power.l2mo, 

Folwell's Water-supply Engineering Svo, 

Frizell's Water-power Svo, 

Fuertes's Water and Public Health 12mo, 

" Water-filtration Works 12mo, 

Ganguillet and Kutter's General Formula for the Uniform 
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rng and Trautwine.) Svo, 

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Hazlehurst's Towers and Tanks for Water-works Svo, 

Herschel's 115 Experiments on the Carrying Capacity of Large, 

Riveted, Metal Conduits Svo, 2 00 



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6 00 


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2 50 


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Mason's Water-supply. (Considered Principally from a Sani- 
tary Standpoint.) 8vo, 4 00 

Merriman's Treatise on Hydraulics 8vo, 4 00 

• Michie's Elements of Analytical Mechanics 8vo, 4 00 

Schuyler's Reservoirs for Irrigation, Water-power, and Domestic 

Water-supply Large Svo, 5 00 

Turneaure and Russell. Public Water-supplies Svo, 5 00 

Wegmann's Design and Construction of Dams 4to, 5 00 

" Water-supply of the City of New York from 1658 to 

1895 4to, 10 00 

Weisbach's Hydraulics and Hydraulic Motors, (Du Bois.) . .8vo, 5 00 

Wilson's Manual of Irrigation Engineering Small Svo, 4 00 

Wolff's Windmill as a Prime Mover Svo, 3 00 

Wood's Turbines .Svo, 2 60 

*' Elements of Analytical Mechanics Svo, 3 00 



MATERIALS OF ENGINEERING. 

Baker's Treatise on Masonry Construction Svo, 

Black's United States Public Works Oblong 4to, 

Eovey's Strength of Materials and Theory of Structures. . . .Svo, 
Burr's Elasticity and Resistance of the Materials of Engineer- 
ing ,. .Svo, 

Byrne's Highway Construction Svo, 

" Inspection of the Materials and Workmanship Em- 
ployed in Construction 16mo, 

Church's Mechanics of Engineering Svo, 

Du Bois's Mechanics of Engineering. Vol. I Small 4to, 

Johnson's Materials of Construction Large Svo, 

Keep's Cast Iron Svo, 

Lanza's Applied Mechanics Svo, 

Martens's Handbook on Testing Materials. (Henning.).2 v., Svo, 

Merrill's Stones for Building and Decoration Svo, 

Merriman's Text-book on the Mechanics of Materials Svo, 

Merriman's Strength of Materials 12mo, 

Metcalf's Steel. A Manual for Steel-users 12mo, 

Patton's Practical Treatise on Foundations Svo, 

Rockwell's Roads and Pavements in France. 12mo, 

Smith's Wire: Its Use and Manufacture Small 4to, 

" Materials of Machines 12mo, 

Snow's Principal Species of Wood : Their Characteristic Proper- 
ties. {In preparation.) 

Spalding's Hydraulic Cement 12mo, 

" Text-book on Roads and Pavements 12mo, 

Thurston's Materials of Engineering 3 Parts, Svo, 

Part I. — Non-metallic Materials of Engineering and Metal- 
lurgy 8vo, 

Part II. — Iron and Steel Svo, 

Part III. — A Treatise on Brasses, Bronzes and Other Alloys 

and Their Constituents Svo, 

Thurston's Text- book of the Materials of Construction Svo, 

Tillson's Street Pavements and Paving Materials Svo, 

Waddell's De Pontibus. (A Pocket-book for Bridge Engineers.) 

16mo, morocco, 3 00 

" Specifications for Steel Bridges 12mo, 1 26 

Wood's Treatise on the Resistance of Materials, and an Ap- 
pendix on the Preservation of Timber Svo, 2 00 

" Elements of Analytical Mechanics Svo, 3 00 

7 



5 00 


5 00 


7 50 


5 00 


5 00 


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6 00 


7 50 


6 00 


2 50 


7 50 


7 50 


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5 00 


1 26 


3 00 


1 00 


2 00 


2 00 


8 00 


2 00 


3 60 


2 60 


5 00 


4 00 



RAILWAY ENGINEERING. 

Andrews's Handbook for Street Railway Engineers. 3x5 in. mor., 1 25 

Berg's Buildings and Structures of American Railroads ... 4to, 5 00 

Brooks's Handbook of Street Railroad Location. . 16mo, morocco, 1 50 

Butts's Civil Engineer's Field-book 16mo, morocco, 2 50 

Crandall's Transition Curve 16mo, morocco, 1 5(3 

" Railway and Other Earthwork Tables 8vo, 1 50 

Dawson's Electric Railways and Tramways . Small 4to, half mor., 12 50 

" " Engineering " and Electric Traction Pocket-book. 

16mo, morocco, 4 00 

Dredge's History of the Pennsylvania Railroad: (1879.) .Paper, 5 00 

* Drioker's Tunneling, Explosive Compounds, and Rock Drills. 

4to, half morocco, 25 00 

Fisher's Table of Cubic Yards Cardboard, 25 

Godwin's Railroad Engineers' Field-book and Explorers' Guide. 

16mo, morocco, 2 50 

Howard's Transition Curve Field-book 16mo, morocco, 1 50 

Hudson's Tables for Calculating the Cubic Contents of Exca- 
vations and Embankments Svo, 1 00 

Nagle's Field Manual for Railroad Engineers. . . .16mo, morocco, 3 00 

Philbrick's Field Manual for Engineers 16mo, morocco, 3 00 

Pratt and Alden's Street-railway Road-bed Svo, 2 00 

Searles's Field Engineering 16mo, morocco, 3 00 

" Railroad Spiral 16mo, morocco, 1 50 

Taylor's Prismoidal Formulae and Earthwork Svo, 1 50 

* Trautwine's Method of Calculating the Cubic Contents of Ex- 

cavations and Embankments by the Aid of Dia- 
grams Svo, 2 00 

* " The Field Practice of Laying Out Circular Curves 

for Railroads 12mo, morocco, 2 50 

* " Cross-section Sheet Paper, 25 

Webb's Railroad Construction Svo, 4 00 

Wellington's Economic Theory of the Location of Railways. . 

Small Svo, 5 00 



DRAWING. 

Barr's Kinematics of Machinery Svo, 2 50 

• Bartlett's Mechanical Drawing Svo, 3 00 

Coolidge's Manual of Drawing Svo, paper, 1 00 

Durley's Elementary Text-book of the Kinematics of Machines. 

{In preparation.) 

Hill's Text-book on Shades and Shadows, and Perspective. . Svo, 2 00 
Jones's Machine Design: 

Part I. — Kinematics of Machinery Svo, 1 50 

Part II. — ^Form, Strength and Proportions of Parts Svo, 3 00 

MacCord's Elements of Descriptive Geometry Svo, 3 00 

" Kinematics; or. Practical Mechanism Svo, 5 00 

" Mechanical Drawing 4to, 4 00 

" Velocity Diagrams Svo, 1 50 

•Mahan's Descriptive Geometry and Stone-cutting Svo, 1 50 

Mahan's Industrial Drawing. (Thompson.) Svo, 3 50 

Reed's Topographical Drawing and Sketching 4to, 5 00 

Reid's Course in Mechanical Drawing Svo, 2 00 

" Text-book of Mechanical Drawing and Elementary Ma- 
chine Design Svo, 3 00 

Robinson's Principles of Mechanism Svo, 3 00 



Smith's Manual of Topographical Drawing. (McMillan.) .8vo, 2 50 
Warren's Elements of Plane and Solid Free-hand Geometrical 

Drawing 12mo, 1 00 

" Drafting Instruments and Operations 12mo, 1 25 

" Manual of Elementary Projection Drawing. .. .12mo, 1 50 
" Manual of Elementary Problems in the Linear Per- 
spective of Form and Shadow 12mo, 1 00 

" Plane Problems in Elementary Geometry 12mo, 1 25 

" Primary Geometry 12mo, 75 

" Elements of Descriptive Geometry, Shadows, and Per- 
spective 8vo, 3 50 

" General Problems of Shades and Shadows 8vo, 3 00 

" Elements of Machine Construction and Drawing. .Svo, 7 50 
" Problems, Theorems, and Examples in Descriptive 

Geometry Bvo, 2 50 

Weisbach's Kinematics and the Power of Transmission. (Hert- 

mann and Klein.) Svo, 5 00 

Wtelpley's Practical Instruction in the Art of Letter En- 
graving 12mo, 2 00 

Wilson's Topographic Surveying Svo, 3 50 

Wilson's Free-hand Perspective Svo, 2 50 

Woolf s Elementary Course in Descriptive Geometry. .Large Svo, 3 00 



ELECTRICITY AND PHYSICS. 

Anthony and Braekett's Text-book of Physics. (Magie.) 

Small Svo, 3 00 
Anthony's Lecture-notes on the Theory of Electrical Measur- 

ments 12mo, 1 00 

Benjamin's History of Electricity Svo, 3 00 

Benjamin's Voltaic Cell Svo, 3 00 

Classen's Qantitative Chemical Analysis by Electrolysis. Her- 

rick and Boltwood.) Svo, 3 00 

Crehore and Squier's Polarizing Photo-chronograph Svo, 3 00 

Dawson's Electric Railways and Tram ways.. Small 4to, half mor., 12 50 
Dawson's " Engineering " and Electric Traction Pocket-book. 

16mo, morocco, 4 00 

Flather's Dynamometers, and the Measurement of Power. . 12nio, 3 00 

Gilbert's De Magnete. (Mottelay.) Svo, 2 50 

Holman's Precision of Measurements Svo, 2 00 

" Telescopic Mirror-scale Method, Adjustments, and 

Tests Large Svo, 75 

Landauer's Spectrum Analysis. (Tingle.) Svo, 3 00 

Le Chatelier's High-temperature Measurements. (Boudouard — 

Burgess.) I2mo, 3 00 

LSb's Electrolysis and Electrosynthesis of Organic Compounds. 

(Lorenz.) 12mo, 1 00 

Lyons's Treatise on Electromagnetic Phenomena Svo, 6 00 

• Michie. Elements of Wave Motion Relating to Sound and 

Light Svo, 4 00 

Niaudet's Elementary Treatise on Electric Batteries (Fish- 
back.) 12mo, 2 50 

• Parshall and Hobart's Electric Generators..Small 4to, half mor., 10 00 
Ryan, Norris, and Hoxie's Electrical Machinery. (In preparation.) 
Tliurston's Stationary Steam-engines Svo, 2 50 

• Tillman. Elementary Lessons in Heat Svo, 1 50 

Tory and Pitcher. Manual of Laboratory Physics .. Small Svo, 2 00 

9 



2 50 


7 00 


7 50 


1 50 


6 00 


6 50 


5 00 


5 50 


3 GO 


2 50 



LAW. 

• Davis, Elements of Law 8vo, 

• " Treatise on the Military Law of United States. .8vo, 

• Sheep, 

Manual for Courts-mai'tial 16mo, morocco, 

Wait's Engineering and Architectural Jurisprudence 8vo, 

Sheep, 
" Law of Operations Preliminary to Construction in En- 
gineering and Architecture Svo, 

Sheep, 

" Law of Contracts Svo, 

Winthrop's Abridgment of Military Law 12mo, 

MANUFACTURES. 

Beaumont's Woollen and Worsted Cloth Manufacture. ...12mo, 1 50 
Bemadou's Smokeless Powder — Nitro-cellulose and Theory of 

the Cellulose Molecule l2mo, 2 50 

BoUand's Iron Founder 12mo, cloth, 2 50 

" " The Iron Founder " Supplement 12mo, 2 50 

" Encyclopedia of Founding and Dictionary of Foundry 

Terms Used in the Practice of Moulding. .. .12mo, 3 00 

Eissler's Modern High Explosives Svo, 4 00 

Eflfront's Enzymes and their Applications. (Prescott.).. .Svo, 3 00 

Fitzgerald's Boston Machinist ISmo, 1 00 

Ford's Boiler Making for Boiler Makers ISmo, 100 

Hopkins's Oil-chemists' Handbook Svo, 3 00 

Keep's Cast Iron Svo 2 50 

Leach's The Inspection and Analysis of Food with Special 
Reference to State Coutrol. {In preparation.) 

Metcalf's Steel. A Manual for Steel-users 12mo, 2 00 

Metcalfs Cost of Manufactures — And the administration of 

Workshops, Public and Private Svo, 5 00 

Meyer's Modern Locomotive Construction 4to, 10 00 

• Reisig's Guide to Piece-dyeing Svo, 25 00 

Smith's Press- working of Metals Svo, 3 00 

" Wire: Its Use and Manufacture Small 4to, 3 00 

Spalding's Hydraulic Cement 12mo, 2 00 

Spencer's Handbook for Chemists of Beet-sugar Houses. 

16mo, morocco, 3 00 
" Handbook for Sugar Manufacturers and their Chem- 
ists 16mo, morocco, 2 00 

Thurston's Manual of Steam-boilers, their Designs, Construc- 
tion and Operation Svo, 5 00 

Walke's Lectures on Explosives Svo, 4 00 

West's American Foundry Practice 12mo, 2 50 

" Moulder's Text-book 12mo, 2 50 

Wiechmann's Sugar Analysis Small Svo, 2 50 

Wolff's Windmill as a Prime Mover. Svo, 3 00 

Woodbury's Fire Protection of Mills Svo, 2 50 

MATHEMATICS. 

Baker's Elliptic Functions Svo, 1 60 

• Bass's Elements of Differential Calculus 12mo, 4 00 

Briggs's Elements of Plane Analytic Geometry 12mo, 1 00 

Chapman's Elementary Course in Theory of EJquationa. . .12mo, 1 50 

Compton's Manual of Logarithmic Computations.. 12mo, I 50 

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Davis's Introduction to the Logic of Algebra 8vo, 1 60 

•Dickson's College Algebra Large 12mo, 1 50 

Halsted's Elements of Geometry 8vo, 1 75 

" Elementary Synthetic Geometry 8vo, 1 50 

•Johnson's Three-place Logarithmic Tables: Vest-pocket size, 

pap., 15 

100 copies for 5 00 

• Mounted on heavy cardboard, 8 X 10 inches, 25 

10 copies for 2 00 
" Elementary Treatise on the Integral Calculus. 

Small 8vo, 1 50 

" Curve Tracing in Cartesian Co-ordinates 12mo, 1 00 

" Treatise on Ordinary and Partial Differential 

Equations Small 8vo, 3 50 

" Theory of Errors and the Method of Least 

Squares 12mo, 1 50 

• " Theoretical Mechanics 12mo, 3 00 

Laplace's Philosophical Essay on Probabilities. CTruscott and 

Emory.) " 12mo, 2 00 

•Ludlow and Bass. Elements of Trigonometry and Logarith- 
mic and Other Tables 8vo, 3 00 

" Trigonometry. Tables published separately. .Each, 2 00 

Merriman and Woodward. Higher Mathematics 8vo, 5 00 

Merriman's Method of Least Squares Svo, 2 00 

Rice and Johnson's Elementary Treatise on the Diflferential 

Calculus Small 8vo, 3 00 

" Differential and Integral Calculus. 2 vols. 

in one Small Svo, 2 50 

Wood's Elements of Co-ordinate Geometry 8vo, 2 00 

" Trigometry: Analytical, Plane, and Spherical. .. .12mo, 1 00 



MECHANICAL ENGINEERING. 

MATERIALS OF ENGINEERING, STEAM ENGINES 
AND BOILERS. 

Baldwin's Steam Heating for Buildings 12mo, 2 60 

Barr's Kinematics of Machinery 8vo, 2 50 

* Bartlett's Mechanical Drawing Svo, 3 00 

Benjamin's Wrinkles and Recipes 12mo, 2 00 

Carpenter's Experimental Engineering Svo, 6 00 

" Heating and Ventilating Buildings Svo, 4 00 

Clerk's Gas and Oil Engine Small Svo, 4 00 

Coolidge's Manual of Drawing Svo, paper, 1 00 

Cromwell's Treatise on Toothed Gearing 12mo, 1 50 

" Treatise on Belts and Pulleys 12mo, 1 50 

Durley's Elementary Text-book of the Kinematics of Machines. 

(In preparation.) 

Slather's Dynamometers, and the Measurement of Power . . 12mo, 3 00 

" Rope Driving 12mo, 2 00 

Gill's Gas an Fuel Analysis for Engineers 12mo, 1 25 

Hall's Car Lubrication 12mo, 1 00 

Jones's Machine Design: 

Part I. — Kinematics of Machinery Svo, 1 50 

Part II. — Form, Strength and Proportions of Parts Svo, 3 00 

Kent's Mechanical Engineers' Pocket-book 16mo, morocco, 5 00 

Kerr's Power and Power Transmission Svo, 2 00 

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3 


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2 


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3 


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MaeCord's Kinematics; or. Practical Mechanism 8vo, 5 00 

" Mechanical Drawing 4to, 4 00 

" Velocity Diagrams 8vo, 

Mahan's Industrial Drawing. (Thompson.) 8vo, 

Poole's Calorific Power of Fuels Svo, 

Reid's Course in Mechanical Drawing Svo, 

" Text-book of Mechanical Drawing and Elementary 

Machine Design Svo, 

Richards's Compressed Air 12mo, 

Robinson's Principles of Mechanism Svo, 

Smith's Press-working of Metals Svo, 

Thurston's Treatise on Friction and Lost Work in Machin- 
ery and Mill Work Svo, 

" Animal as a Machine and Prime Motor and the 

Laws of Energetics 12mo, 

Warren's Elements of Machine Construction and Drawing. .Svo, 
Weisbach's Kinematics and the Power of Transmission. (Herr- 
mann—Klein.) Svo, 

" Machinery of Transmission and Governors. (Herr- 
mann—Klein.) Svo, 

" Hydraulics and Hydraulic Motors. (Du Bois.) .Svo, 

Wolff's Windmill as a Prime Mover Svo, 

Wood's Turbines Svo, 

MATERIALS OF ENGINEERING. 

Bovey's Strength of Materials and Theory of Structures. .Svo, 7 50 
Burr's Elasticity and Resistance of the Materials of Engineer- 
ing Svo, 5 00 

Church's Mechanics of Engineering Svo, 6 00 

Johnson's Materials of Construction Large Svo, 6 00 

Keep's Cast Iron Svo, 2 50 

Lanza's Applied Mechanics Svo, 7 50 

Martens's Handbook on Testing Materials. (Henning.) Svo, 7 50 

Merriman'a Text-book on the Mechanics of Materials Svo, 4 00 

" Strength of Materials 12mo, 1 GO 

Metcalf's Steel. A Manual for Steel-users 12mo, 2 00 

Smith's Wire: Its Use and Manufacture Small 4to, 3 00 

" Materials of Machines 12mo, 1 00 

Thurston's Materials of Engineering 3 vols., Svo, 8 00 

Part IL— Iron and Steel Svo, 3 50 

Part III. — A Treatise on Brasses, Bronzes and Other Alloys 

and their Constituents Svo, 2 50 

Thurston's Text-book of the Materials of Construction Svo, 5 00 

Wood's Treatise on the Resistance of Materials and an Ap- 
pendix on the Preservation of Timber Svo, 2 00 

" Elements of Analytical Mechanics Svo, 3 00 

STEAM ENGINES AND BOILERS. 

Camot's Reflections on the Motive Power of Heat. (Thurston.) 

12mo, 1 50 
Dawson's " Engineering " and Electric Traction Pocket-book. 

16mo, morocco, 4 00 

Ford's Boiler Making for Boiler Makers ISmo, 1 00 

Goss's Locomotive Sparks Svo, 2 00 

Hemenway's Indicator Practice and Steam-engine Economy. 

12mo, 2 00 

Button's Mechanical Engineering of Power Plants Svo, 5 00 

" Heat and Heat-engines Svo, 5 00 

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Kent's Steam-boiler Economy 8vo, 4 00 

Kneass's Practice and Theory of the Injector 8vo, 1 50 

MacCord's Slide-valves 8vo, 2 00 

Meyer's Modern Locomotive Construction 4to, 10 00 

Peabody's Manual of the Steam-engine Indicator 12mo, 1 50 

" Tables of the Properties of Saturated Steam and 

Other Vapors 8vo, 1 00 

" Thermodynamics of the Steam-engine and Other 

Heat-engines 8vo, 5 00 

" Valve-gears for Steam-engines 8vo, 2 50 

Peabody and Miller. Steam-boilers 8vo, 4 00 

Pray's Twenty Years with the Indicator Large 8vo, 2 50 

Pupin's Thermodynamics of Reversible Cycles in Gases and 

Saturated Vapors. (Osterberg.) 12mo, 1 25 

Reagan's Locomotive Mechanism and Engineering 12mo, 2 00 

Rontgen's Principles of Thermodynamics. (Du Bois.) 8vo, 5 00 

Sinclair's Locomotive Engine Running and Management. . 12mo, 2 00 

Smart's Handbook of Engineering Laboratory Practice. .12mo, 2 50 

Snow's Steam-boiler Practice 8vo, 3 00 

Spangler's Valve-gears 8vo, 2 50 

" Notes on Thermodynamics 12mo, 1 00 

Thurston's Handy Tables 8vo, 1 50 

" Manual of the Steam-engine 2 vols., 8vo, 10 00 

Part I. — History, Structure, and Theory 8vo, 6 00 

Part II. — Design, Construction, and Operation Bvo, 6 00 

Thurston's Handbook of Engine and Boiler Trials, and the Use 

of the Indicator and the Prony Brake 8vo, 5 00 

" Stationary Steam-engines 8vo, 2 50 

'* Steam-boiler Explosions in Theory and in Prac- 
tice 12mo, 1 50 

" Manual of Steam-boilers, Their Designs, Construc- 
tion, and Operation 8vo, 5 00 

Weisbach's Heat, Steam, and Steam-engines. (Du Bois.) . .8vo, 5 00 

Wbitham's Steam-engine Design 8vo, 5 00 

Wilson's Treatise on Steam-boilers. (Flather.) I6mo, 2 50 

Wood's Thermodynamics, Heat Motors, and Refrigerating 

Machines • -Svo, 4 00 

MECHANICS AND MACHINERY. 

Barr's Kinematics of Machinery 8vo, 2 50 

Bovey's Strength of Materials and Theory of Structures. .8 vo, 7 50 

Chordal.— Extracts from Letters 12rao, 2 00 

Church's Mechanics of Engineering 8vo, 6 00 

" Notes and Examples in Mechanics 8vo, 2 00 

Compton's First Lessons in Metal-working 12mo, 1 50 

Compton and De Groodt. The Speed Lathe 12mo, 1 60 

Cromwell's Treatise on Toothed Gearing 12rao, 1 50 

" Treatise on Belts and Pulleys 12m o, 1 50 

Dana's Text-book of Elementary Mechanics for the Use of 

Colleges and Schools 12mo. 1 50 

Dingey's Machinery Pattern Making 12ino, 2 00 

Dredge's Record of the Transportation Exhibits Building of the 

World's Columbian Exposition of 1893 4to, half mor., 5 00 

Du Bois's Elementary Principles of Mechanics: 

Vol. I.— Kinematics 8vo. 3 50 

Vol. II.— Statics 8vo, 4 00 

Vol. III.— Kinetics ^^"' ■; ^'' 

Du Bois's Mechanics of Engineering. Vol. 1 Small 4to, 7 50 

« « « .« « Vol.11 Small 4to, 10 00 

13 



Durley's Elementary Text-book of the Kinematics of Machines. 

(In preparation.) 

Fitzgerald's Boston Machinist 16mo, 1 00 

Flather's Dynamometers, and the Measurement of Power. 12mo, 3 00 

" Rope Driving 12mo, 2 00 

Goss's Locomotive Sparks 8vo, 2 00 

Hall's Car Lubrication 12mo, 1 00 

Holly's Art of Saw Filing 18mo, 75 

* Johnson's Theoretical Mechanics 12mo, 3 00 

Johnson's Short Course in Statics by Graphic and Algebraic 

Methods. {In preparation.) 
Jones's Machine Design: 

Part I. — ^Kinematics of Machinery 8vo, 1 50 

Part II. — Form, Strength and Proportions of Parts; .. .Svo, 3 00 

Kerr's Power and Power Transmission Svo, 2 00 

Lanza's Applied Mechanics. Svo, 7 50 

MacCord's Kinematics; or, Practical Mechanism Svo, 5 00 

" Velocity Diagrams Svo, 1 50 

Merriman's Text-book on the Mechanics of Materials Svo, 4 00 

* Miehie's Elements of Analytical Mechanics Svo, 4 00 

Reagan's Locomotive Mechanism and Engineering 12mo, 2 00 

Reid's Course in Mechanical Drawing Svo, 2 00 

" Text-book of Mechanical Drawing and Elementary 

Machine Design Svo, 3 00 

Richards's Compressed Air 12mo, 1 50 

Robinson's Principles of Mechanism Svo, 3 00 

Ryan, Norris, and Hoxie's Electrical Machinery. {In preparation.) 

Sinclair's Locomotive-engine Running and Management. .12mo, 2 00 

Smith's Press-working of Metals Svo, 3 00 

" Materials of Machines 12mo, 1 00 

Thurston's Treatise on Friction and Lost Work in Machin- 
ery and Mill Work Svo, 3 00 

" Animal as a Machine and Prime Motor, and the 

Laws of Energetics 12mo, 1 00 

Warren's Elements of Machine Construction and Drawing. .Svo, 7 50 
Weisbach's ELinematics and the Power of Transmission. 

(Herrman — Klein.) Svo, 5 00 

" Machinery of Transmission and Governors. (Herr- 

(man — ^Klein.) Svo, 6 00 

Wood's Elements of Analytical Mechanics Svo, 3 00 

" Principles of Elementary Mechanics 12mo, 1 25 

" Turbines Svo, 2 50 

The World's Columbian Exposition of 1893 4to, 1 00 

METALLURGY. 

Egleston's Metallurgy of Silver, Gold, and Mercury: 

Vol. I.-Silver Svo, 7 50 

Vol. 11. — Gold and Mercury Svo, 7 50 

** Iles's Lead-smelting 12mo, 2 50 

Keep's Cast Iron Svo, 2 50 

Kunhardt's Practice of Ore Dressing in Lurope Svo, 1 50 

Le Chatelier's High- temperature Measurements. (Boudouard — 

Burgess.) 12mo, 3 00 

Metcalf's Steel. A Manual for Steel-users 12mo, 2 00 

Smith's Materials of Machines 12mo, 1 00 

Thurston's Materials of Engineering. In Three Parts Svo, S 00 

Part II. — Iron and Steel Svo, 3 5U 

Part III.— A Treatise on Brasses, Bronzes and Other Alloys 

and Their Constituents Svo, 2 50 

14 



MINERALOGY. 

Barringer's Description of Minerals of Commercial Value. 

Oblong, morocco, 2 50 

Boyd's Resources of Southwest Virginia 8vo, 3 00 

" Map of. Southwest Virginia Pocket-book form, 2 GO 

Brush's Manual of Determinative Mineralogy. (Penfield.) .8vo, 4 00 

Chester's Catalogue of Minerals. 8vo, paper, 1 00 

Cloth, 1 25 

" Dictionary of the Names of Minerals Svo, 3 50 

Dana's System of Mineralogy Large Svo, half leather, 12 50 

" First Appendix to Dana's New " System of Mineralogy." 

Large 8vo, 1 00 

" Text-book of Mineralogy Svo, 4 00 

" Minerals and How to Study Them 12mo, 1 50 

" Catalogue of American Localities of Minerals. Large 8vo, 1 00 

" Manual of Mineralogy and Petrography 12mo, 2 00 

Egleston's Catalogue of Minerals and Synonyms 8vo, 2 50 

Hussak's The Determination of Eock-forming Minerals. 

(Smith.) Small Svo, 2 00 

• Penfield's Notes on Determinative Mineralogy and Record of 

Mineral Tests Svo, paper, 50 

Rosenbusch's Microscopical Physiography of the Rock-making 

Minerals. (Idding's.) Svo, 5 00 

•Tillman's Text-book of Important Minerals and Rocks.. Svo, 2 00 

Williams's Manual of Lithology Svo, 3 00 



MINING. 

Beard'8 Ventilation of Mines 12mo, 2 50 

Boyd's Resources of Southwest Virginia Svo, 3 00 

" Map of Southwest Virginia Pocket-book form, 2 00 

• Drinker's Timneling, Explosive Compounds, and Rock 

Drills 4to, half morocco, 25 00 

Eissler's Modern High Explosives Svo, 4 00 

Fowler's Sewage Works Analyses 12mo, 2 00 

Goodyear's Coal-mines of the Western Coast of the United 

States 12mo, 2 50 

Ihlseng's Manual of Mining Svo, 4 00 

** Hes's Lead-smelting 12mo, 2 50 

Kunhardt's Practice of Ore Dressing in Europe .8vo, 1 50 

O'DriscoU's Notes on the Treatment of Gold Ores Svo, 2 00 

Sawyer's Accidents in Mines Svo, 7 00 

Walke's Lectures on Explosives Svo, 4 00 

Wilson's Cyanide Processes 12mo, 1 50 

Wilson's Chlorination Process 12mo, 1 50 

Wilson's Hydraulic and Placer Mining 12mo, 2 00 

Wilson's Treatise on Practical and Theoretical Mine Ventila- 
tion 12mo, 1 25 

SANITARY SCIENCE. 

■Fol well's Sewerage. (Designing, Construction and Maintenance.) 

Svo, 3 00 

" Water-supply Engineering Svo, 4 00 

iFuertes's Water and Public Health 12mo, 1 50 

" Water-filtration Works 12mo, 2 50 

15 



Gerhard's Guide to Sanitary House-inspection 16mo, 1 00 

Goodrich's Economical Disposal of Towns' Refuse . . . Demy 8vo, 3 50 

Hazen's Filtration of Public Water-supplies 8vo, 3 00 

Kiersted's Sewage Disposal 12mo, 1 25 

Leach's The Inspection and Analysis of Food with Special 

Eeference to State Control. {In preparation.) 
Mason's Water-supply. (Considered Principally from a San- 
itary Standpoint. 3d Edition, Rewritten 8vo, 4 00 

" Examination of Water. (Chemical and Bacterio- 
logical.) 12mo, 1 25 

Merriman's Elements of Sanitary Engineering Svo, 2 00 

Nichols's Water-supply. (Considered Mainly from a Chemical 

and Sanitary Standpoint.) (1883.) Svo, 2 50 

Ogden's Sewer Design 12mo, 2 00 

* Price's Handbook on Sanitation 12mo, 1 50 

Richards's Cost of Food. A Study in Dietaries 12rao, 1 00 

Richards and Woodman's Air, Water, and Food from a Sani- 
tary Standpoint Svo, 2 00 

Richards's Cost of Living as Modified by Sanitary Science. 12mo, 1 00 

* Richards and Williams's The Dietary Computer Svo, 1 50 

Rideal's Sewage and Bacterial Purification of Sewage Svo, 3 50 

Turneaure and Russell's Public Water-supplies Svo, 5 00 

^Tiipple's Microscopy of Drinking-water Svo, 3 50 

Woodhull's Notes on Military Hygiene 16mo, 1 50 



MISCELLANEOUS. 

Barker's Deep-sea Soundings Svo, 2 00 

EmmoiiS's Geological Guide-book of the Rocky Mountain Ex- 
cursion of the International Congress of Geologists. 

Large Svo, 1 50 

Ferrel's Popular Treatise on the Winds Svo, 4 00 

Haines's American Railway Management 12mo, 2 50 

Mott's Composition, Digestibility, and Nutritive Value of Food. 

Mounted chart, 1 25 

" Fallacy of the Present Theory of Sound 16mo, 1 00 

Ricketts's History of Rensselaer Polytechnic Institute, 1824- 

1894 Small Svo, 3 00 

Rotherham's Emphasised New Testament Large Svo, 2 00 

" Critical Emphasised New Testament 12mo, 1 50 

Steel's Treatise on the Diseases of the Dog Svo, 3 50 

Totten's Important Question in Metrology Svo, 2 50 

The World's Columbian Exposition of 1893 4to, 1 00 

Worcester and Atkinson. Small Hospitals, Establishment and 
Maintenance, and Suggestions for Hospital Architecture, 

with Plans for a Small Hospital 12mo, 1 25 



HEBKEW AND CHALDEE TEXT-BOOKS. 

Green's Grammar of the Hebrew Language Svo, 3 00 

" Elementary Hebrew Grammar 12mo, 125 

" Hebrew Chrestomathy Svo, 2 00 

Gesenius's Hebrew and Chaldee Lexicon to the Old Testament 

Scriptures. (Tregelles.) Small 4to, half morocco, 5 00 

Letteris's Hebrew Bible , . . Svo, 2 25 

16 
















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